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Advanced OrganicComposite Materials forAircraft Structures-Future Program

Committee on the Status and Viability of Composite

Aeronautics and Space Engineering Board

Commission on Engineering and Technical Systems

National Research Council

Materials for Aircraft Structures

NATIONAL ACADEMY PRESSWashington, D.C. 1987

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NOTICE: Th e project tha t is the subject of this report was approved by the Governing Boardof the National Research Council, whose members are drawn from the councils of the NationalAcademy of Sciences, the National Academy of Engineering, and the Inst itu te of Medicine. Th emembers of the committee responsible for the report were chosen for their special competencesand with regard for appropriate balance.

This report has been reviewed by a group other than the authors according to proceduresapproved by a Report Review Committee consisting of members of the National Academy of

Sciences, the National Academy of Engineering, and the Inst itute of Medicine.

Th e National Academy of Sciences is a private, nonprofit, self-perpetuating society of dis-tinguished scholars engaged in scientific and engineering research, dedicated to the furtheranceof science and technology and to their use for the general welfare. Upon the authority of thecharter granted to it by the Congress in 1863, the Academy has a mandate that requires it toadvise the federal government on scientific and technical matters. Dr. Frank Press is presidentof the National Academy of Sciences.

The National Academy of Engineering was established in 1964, under the charter ofth e National Academy of Sciences, as a parallel organization of outstanding engineers. It isautonomous in its administration and in the selection of its members, sharing with the NationalAcademy of Sciences the responsibility for advising the federal government. The NationalAcademy of Engineering also sponsors engineering programs aimed at meeting national needs,encourages education and research, and recognizes the superior achievements of engineers. Dr.

Robert M. White is president of the National Academy of Engineering.The Institute of Medicine was established in 1970 by the National Academy of Sciences

to secure the services of eminent members of appropriate professions in the examination ofpolicy matters pertaining to the health of the public. The Inst itute acts under the responsibilitygiven to the National Academy of Sciences by ita congressional charter to be an adviser to thefederal government and, upon its own initiative, to identify issues of medical care, research,and education. Dr. Samuel 0. Thier is president of the Institute of Medicine.

Th e National Research Council was organized by the National Academy of Sciences in1916 o associate the broad community of science and technology with the Academy's purposesof furthering knowledge and advising the federal government. Functioning in accordance withgeneral policies determined by the Academy, the Council has become the principal operatingagency of both t he National Academy of Sciences and the National Academy of Engineering inproviding services to the government, the public, and the scientific and engineering communities.The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Frank

Press and Dr. Robert M. White are chairman and vice-chairman, respectively, of th e NationalResearch Council.

This report and the study on which it is based were supported by Contract No. NASW-4003 between the National Aeronautics and Space Administration and the National Academyof Sciences.

Copies of this publication are available from:

Aeronautics and Space Engineering BoardNational Research Council2101 Constitution Avenue, NWWashington, DC 20418

Printed in the United States of America

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COMMITTEE ON THE STATUS AND VIABILITY OF

COMPOSITE MATERIALS FOR AIRCRAFT STRUCTURES

JAMES W. MAR (Chuirrnun) ,Jerome C. Hunsaker Professor of Aerospace

Education, Department of Aerospace and Astronautics, Massachusetts

Institute of Technology

RICHARD ABBOTT, Principal Staff Engineer, R&D Division, Beech AircraftCorporation

E. DWIGHT BOUCHARD, Director, Engineering Technology, Structures,

McDonnell Aircraft Company

JON B. DEVAULT, Vice-president and General Manager, Graphite Materials and

Composite Structures, Hercules Aerospace Division

STANLEY MARTIN, JR., Vice-president, V-22 Engineering, Bell Helicopter

Text ron

R. BYRON PIPES, Dean of Engineering, University of Delaware

GEORGE S. SPRINGER, Professor of Aeronautics and Astronautics, Department

MORRIS A. STEINBERG, Consultant; Vice-President-Science, Lockheed

CHARLES F. TIFFANY, Vice-president, Advanced Systems, Boeing Military

of Aeronautics and Astronautics, Stanford University

Corporation (Retired)

Airplane Company

BERNARD MAGGIN, Study Director

Government Liaison Representatives

RICHARD L. BALLARD, Associate Division Chief, Aviation Systems Division,

KEITH I. COLLIER, Deputy for Development Plans, U.S. Air ForceL

JAMES MATTICE, Deputy Director, AFWAL/CD, Wright Patterson Air Force

DANIEL MULVILLE, Structures Technology Manager, Naval Air Systems

JOSEPH R. SODERQUIST, National Resource Specialist, Advanced Nonmetallic

SAMUEL L. VENNERI, Director, Materials and Structures Division, Office of

Department of the Army

Base'

Command

Materials, Federal Aviation Administration

Aeronautics and Space Technology, Headquarters, National Aeronautics and

Space Administration

Aeronautics and Space Administration

LOUIS VOSTEEN, Chief, Materials Division, Langley Research Center, National

'James Mattice replaced Keith I. Collier during the study.

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AERONAUTICS AND SPACE ENGINEERING BOARD

JAMES J. KRAMER ( Chairman),Manager, Advanced Technology Programs,

JOSEPH F. SHEA (Past Chairman), Senior Vice-president, Engineering,

MAX E. BLECK, Vice-president and Assistant to the President, Beech Aircraft

BERNARD BUDIANSKY, Professor of Structural Mechanics, Harvard University

W. BOWMAN CUTTER 111,Coopers and Lybrand

R. RICHARD HEPPE, President, Lockheed-California Company

RICHARD W. HESSELBACHER, Manager, Advanced Development and

KENNETH F. HOLTBY, Senior Vice-president, The Boeing Company

DONALD J. LLOYD-JONES, President and Chief Operating Officer, Western

Airlines

STEPHEN F. LUNDSTROM, Vice-president and Program Director, ParallelProcessing Program, MCC

ARTUR MAGER, Consult ant

STANLEY MARTIN, JR., Vice-president, V-22 Engineering, Bell Helicopter

JOHN L. McLUCAS, Executive Vice-president and Chief Strategic Officer,

FRANKLIN K. MOORE, Joseph C. Ford Professor of Mechanical Engineering,

GEORGE W. MORGENTHALER, Director, Engineering Research Center,

General Electric Company

Raytheon Company

Corporation

Information Systems, Space Systems Division, General Electric Company

Textron

Comsat (Retired)

Cornel1 University

Associate Dean, College of Engineering and Applied Science, The University of

Colorado

University of Kansas

Company, McDonnell Douglas Corporation

Stanford University

JAN ROSKAM, Ackers Distinguished Professor of Aerospace Engineering,

ROGER D. SCHAUFELE, Vice-president, Engineering, Douglas Aircraft

RICHARD S. SHEVELL, Professor, Department of Aeronautics and Astronautics,

ROBERT E. SKELTON, Professor of Aeronautics Engineering, Purdue University

ALTON D. SLAY, Slay Enterprises, Inc.

MORRIS A. STEINBERG, Consultant; Vice-President-Science, Lockheed

LAURENCE R. YOUNG, Professor of Aeronautics and Astronautics,Corporation (Retired)

Massachusetts Institute of Technology

Executive Staff

Robert H. Korkegi, Director

JoAnn Clayton, Senior Program Officer

Bernard Maggin, Senior Program Officer

Anna L. Farrar, Administrative Assistant

Jennifer T. Estep, Administrative Secretary

Regina F. Miller, Senior Secretary

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Acknowledgments

The committee is deeply indebted to the individuals who provided valuable

assistance in this study. They are noted here with their affiliations.

Carl Albrecht, Boeing-Vertol Company

James N. Burns, Hercules Aerospace

Richard L. Circle, Lockheed-Georgia Company

Thomas E. Condon, U.S.Army Jon B. DeVault, Hercules Aerospace

David Forest, Ferro Corporation

Richard N. Hadcock, Grumman Aircraft Systems Division

John B. Hammond, Lockheed-California Company

John V. Harrington, U S . Air ForcePhilip Haselbauer, U S . Army

Charles F. Herndon, General Dynamics Corporation

Joseph Janis, Trans World Airlines

Bruce F. Kay, Sikorsky Aircraft

Leslie M. Lackman, Rockwell Corporation

Joseph K. Lees, E. I. DuPont de Nemours and Company

Thomas W . Longmire, Union Carbide

John E. McCarty, Boeing Military Airplane Company

Jay Meyers, U.S.NavyJMarine Corps

John T. Quinlivan, Boeing Commercial Airplane Company

Theodore Reinhart, U.S.Air Force

David Roselius, US.Air Force

Hassel C. Schjelderup, Douglas Aircraft Company

James H. Starnes, Langley Research Center, National Aeronautics and Space

Keith Stevenson, Bell Helicopter Textron

Administration

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Conrad Trulson, Union Carbide

Ralph M. Verette, McDonnell Douglas Helicopter Company

Curtis Walker, Delta Airlines

James Waller, U.S. Army

Herbert Wardell, Gulfstream American

Robin S.Whitehead, Northrop Aircraft DivisionHavard A. Wood, Headquarters, National Aeronautics and Space Administrat ion

In addition, special thanks are due A. J. Evans, past executive director of the

Aeronautics and Space Engineering Board, for his preparatory work leading to the

definition of this study and the organization of the committee, and to Julie Ferguson

for her dedication and support in the early stages of this study.

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Preface

At the request of the National Aeronautics and Space Administration’s Office

of Aeronautics and Space Technology, the National Research Council’s Aeronautics

and Space Engineering Board established a committee to undertake an examination

of the sta tus of advanced organic composite material for aircraft structures. The

committee’s tasks were to assess the state of this technology and t o identify the

research and technology development actions that would assist in the acceleration

of the application of this material in production aircraft.

The tasks of the committee were accomplished through deliberations following a

series of reviews of government and industry experience and activity, and committee

discussions of benefits, inhibiting factors, technology development needs, and possi-

ble government action. The work of the committee is summarized in the body of the

report , which provides background related to the field of organic composites and of

this study, including the approach used by the committee to exercise its t ask . These

chapters of the report are followed by brief discussions of the committee’s findings

and recommendations. The report itself is supplemented by summaries of the work

of the committee related to their views on benefits and technology needs, govern-

ment agency dialogue on issues, questions and technology needs, and a synopsis of

the presentations made to the committee. These materials were used to develop the

findings and recommendations presented in the report.

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Contents

1. INTRODUCTION ..................................................................... 1

2. STUDY CHARTER AND METHODOLOGY ..................................... 3

3. DISCUSSION AND FINDINGS ..................................................... 5

4. RECOMMENDATIONS ............................................................ 12

BIBLIOGRAPHY ........................................................................ 15

SUPPLEMENT: SUMMARY OF COMMITTEE STUDY .......................... 17

Section I-Program Assessment . . . . . . . .19

Aircraft Applications, 19

Material Manufacturers, 26

Government Agencies, 29

Summary of Key Observations, 34

Future R&T Program, 36

Programmatic Matters, 37

Government Programs, 41

Section 11-Response to Government Issues and Questions .. . . . .36

APPENDMES

A. Synopsis of Presentations to the Committee.. . . . . ..43

Application and Operating Experience,43

Application and Flight Experience, 45

Certification and Operational Experience,46

Research and Technology Programs, 47

Industry Forum of February 10-11, 986,52

Large Transports, 52

Committee Meeting of December 17-18,1985,43

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Rotorcraft, 57High-Performance Aircraft, 61

Business Aircraft, 72

Airlines, 76Material Suppliers, 76

Technology Needs and Budget, 83Committee Summary of RT&D Needs and Budgets, 91

Materials Manufacturing-Tailoring and Related Costs, 91

Logistic Support,95

Airline Perspective, 96

Committee Meeting of March 26, 1986,83

B. Correspondence-Air Transport Association of America . . . . 99

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List of Tables and Figures

TABLES

s-1-1

s-1-2

S-1-3

S-1-4

S-1-5

S-1-6

S-1-7

S-1-8

s-11-1

A- 1A-2

A-3

A-4

A-5

A-6

A-7

Potential Advantages .......................................................... 20

Inhibiting Factors .............................................................. 22

Needs............................................................................ 24

Possible Government Action ................................................. 27

Summary Observat ons-Materials .......................................... 28

Individual Government Agency Views on Advanced Organic

Composite Technology Development Needs ................................ 30

Summary of Government Agency Views on Advanced Organic

Composite Technology Development Factors ............................... 31

Government Agency Summary-Technology Program Considerat ons,

All Aircraft Classes............................................................ 33

Representative Costs of Composites for Transport and

Fighter Aircraft ................................................................ 38

Performance Comparisons of Metal and Composite Rotor Blades.......58

Critical Material Properties Proposed for High-Temperature

Composites ..................................................................... 71

Composite Material Business Projection .................................... 77Advanced Organic Composite Research, Technology, and

Development Needs-Government View .................................... 84

Government Advanced Organic Composite Research andTechnology Programs ......................................................... 86

FAA Program Plans-Desired and Actual .................................. 89

Integrated Advanced Organic Composite Research, Technology, and

Development Needs-Government View .................................... 92

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A-8

A-9

A-10

Government Advanced Organic Composite Program Plan. FY 1986 ....93

Government Advanced Organic Composite Program Plan. FY 1987 . . . .93

Government Advanced Organic Composite Program by Element,

FY 1986 and FY 1987 ......................................................... 94

FIGURES-11-1 Data-base development concept .............................................. 40

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1Introduction

Revolutionary advances in structural materials have been responsible for revo-

lutionary changes in all fields of engineering. These advances have had and are still

having a significant impact on aircraft design and performance. Early aircraft con-

struction involved wood, fabric, and wire, which later gave way to metals, notably

aluminum. Aluminum has given way to selected use of other higher-strength metals

(titanium, steel, and superalloys), and both are giving way, to a significant degree,

to composite materials.

Composites are engineered materials. Their properties are tailored through the

use of a mix or blend of different constituents to maximize selected properties of

strength and/or stiffness at reduced weights. A common composite approach is

to use a matrix or host material reinforced by a fibrous second material. Thesecomposites can be ceramic, polymer, or metal based, or mixtures of these materials.

Of special interest in this s tudy are filamentary (organic) polymer systems, herein

commonly referred to as advanced organic composites.

More than 20 years have passed since the potentials of filamentary composite

materials were identified. In a report dated July 1964, the Scientific Advisory Board

of the U.S.Air Force recommended the intense development of boron filaments. The

board identified significant gains in aircraft weapon-system performance through

application of boron composites because of their low densities and high strengths

and stiffnesses per unit of mass.

During the 1970s, however, much lower-cost carbon filaments became a realityand gradually designers turned from boron to carbon composites. By 1971, there was

so much unfettered enthusiasm for carbon epoxy th at 16 suppliers were marketing

over 50 brands of carbon-epoxy preimpregnated (prepreg) materials. The boron-

epoxy material system was developed with substantial assistance and direction from

the government through the Air Force Materials Laboratory, but the carbon-epoxy

material system received only limited government assistance and direction.

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2

The list of composite achievements over the past two decades is long and im-

pressive. Two high-performance military airplanes, the F-18 and AV-8B, currently

in production, utilize carbon-epoxy for 10 percent and 26 percent of their structural

weight, respectively. These carbon-epoxy percent ages include appreciable portions

of the primary struc tural elements of the wings, empennages, and control surfaces

of these aircraft. Two new transports, the Boeing 757 and 767, each use about 3,000pounds of carbon-epoxy in rudders, elevators, and spoilers. Two aircraft under de-

velopment, the U.S.Navy Osprey V-22 and the Beech Aircraft Starship, merit the

appellation “all-composite” because nearly all of the structural components that can

gainfully use composites are made of composites.

Despite these and other examples, filamentary composites still have significant

unfulfilled potential for increasing aircraft productivity; the rendering of advanced

organic composite materials into production aircraft structures has been disappoint-

ingly slow. This report addresses why and recommends research and technology de-

velopment actions tha t will assist in accelerating the application of advanced organic

composites to production aircraft.

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2Study Charter and Methodology

Late in 1985, the Aeronautics and Space Engineering Board of the National

Research Council, at the request of the National Aeronautics and Space Adminis-

tration’s (NASA) Office of Aeronautics and Space Technology, formed a committee

that was chartered to assess the status and viability of organic composite tech-

nology for aircraft structures. The charter directed the committee to concentrate

on advanced organic composites. The committee was to make recommendations

concerning ways tha t federally sponsored research and technology development pro-

grams could produce a more rapid and timely translation of the potential of these

composites into production aircraft. The committee responded to this charter by:

1. Reviewing pertinent government aircraft application, design, production,

and service experience with advanced organic composites. Agencies included NASA,

the Federal Aviation Administration, and the U.S. Army, Air Force, and Navy.

Conducting a forum at which aerospace engineers from prominent design,

manufacturing, and operating industrial segments (transports, airline operators,

rotorcraft, high-performance aircraft, general aviation, and material producers) pre-

sented their views on status, viability, future applications, and technology develop-

ment needs.

Reviewing ongoing federal research and development programs and the per-

ceptions of the various government agencies of issues germane to future applications

and technology development program needs.

Conducting a workshop to assess critically the data and opinions amassedduring steps 1 , 2 , and 3 and to prepare an outline and a rough draft of this report.

2.

3.

4.

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4

The committee arrived at its findings and developed recommendations through

an examination of the following aspects of advanced organic composite material

technology:

Potential benefits

Inhibiting factors

Needs for technology development

Possible government actions

The committee found it convenient to partition the “universe”of this study into

the following elements:

Large transports

Rotorcraft

High-performance aircraft

General aviation

aswell as

Materials

Airline operators

A summary of the committee’s examination of these complex matters is pre-

sented in the report’s Supplement. The Supplement has two parts: (1) Program

Assessment; and (2) Response to Government Issues and Questions. A Synopsis of

Presentations to the Committee is presented in Appendix A. The committee arrived

at its findings and recommendations through deliberation and its workshop activity.

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3Discussion and Findings

AIRCRAFT DIFFERENCES

There are appreciable differences in the structural requirements and usage of

the four classes of aircraft addressed: large transports, high-performance military

aircraft, rotorcraft, and general aviation aircraft. Large commercial transports are

designed to a limit-load factor of 2.5 g, compared to 9 g for high-performance

military aircraft. Large commercial transports fly 10 or more hours a day and

experience thousands of takeoffs and landings through their lifetime. As a result

their pressurized fuselages experience loads approaching limit load thousands oftimes. High-performance military aircraft fly only 20 to 40 hours a month during

peacetime and reach or exceed limit load relatively few times-in the hundreds-

during their lifetime. The design longevity of a transport is upward of 40,000 flight

hours whereas high-performance military aircraft have a design life of some 6,000 to

8,000 flight hours.

Rotorcraft, both military and civil, are designed for relatively low limit-load

factors of 2.5 g to 3.0 g and are often flown at or close to these limits. The rotorcraft

design problem is complicated by the wide spectrum of vibratory loads imposed by

different speed regimes and associated design limitations as well as the high degree

of maintenance required.

General aviation aircraft, the Federal Aviation Administration’s (FAA) category

for aircraft whose takeoff gross weight is under 12,500pounds, are lightly loaded and

are maintained by an infrastructure that is much different from large transports

or military aircraft. Their structural design is dominated by stiffness rather than

strength.

These factors aswell asothers lead to structural configurations and design detail

that are unique for each of the four classes of aircraft. Thus, fo r example, it is

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basically not practical to scale up geometrically a general aviation aircraft into a

large transport or vice versa. Despite these differences, there are similarities in the

potential benefits, inhibiting factors, needs for technology development, and possible

government actions with respect to advanced organic composite material research

and technology.

MEASURES OF PERFORMANCE

Range and maneuverability are two of the traditional measures of aircraft per-

formance. The benefits of a lower structural weight fraction are quantified by the

Breguet range and specific excess-power equations. Both of these equations contain

only aircraft performance variables. For example, the Breguet equation will show

either the increase in range attendant to reduced structural weight for the same

gross-weight airplane or the same range for an airplane of less gross weight.

Previous advanced composite research, technology, and development programs

have focused on improvements in these kinds of aircraft performance parameters.Neither the Breguet range equation nor the specific excess-power equation addresses

improved aircraft system capability. Here, for example, structural weight savings can

. be used for increasing mission capability, such as adverse weather flight, wind-shear

warning, collision avoidance, category 3 landings, and air-freight adaptation, and for

modifying military aircraft with equipment to cope with increasingly sophisticated

enemy defenses. Thus, more and more avionics are being put into all classes of

airplanes.

Structural weight savings for future military aircraft can be expected t o allow

multipurpose capability; for example, the same basic airplane could be called upon to

fulfill attack, air defense, and interdiction missions. Additionally, stealth, a futurerequirement, places special demands upon the application of organic materials.

For civil aircraft, structural weight savings can be translated into reduced direct

operating costs resulting in lower passenger seat-mile or cargo ton-mile costs.

Structural integrity directed at providing greater absolute safety is another

evolving factor that requires increased attention to design detail. An example is

the recent addition of the damage tolerance concept to the federal aviation regula-

tions. This new regulation could result in more structural weight as well as many

more engineering hours for design and testing.

These aircraft system requirement trends tend to increase takeoff gross weight,

although the traditional performance requirements (measures),such as range, takeoff

distance, altitude, and cruise speed, remain the same or call for improvements.

Unless new technology is forthcoming, these more capable aircraft will be larger,

heavier, and require more propulsive power, thereby becoming less productive. It

is for this reason that advanced composites of all kinds-metals as well as organics

and combinations-have a unique future role. They can provide the designer with

the ability to reduce structural weight significantly, allowing the addition of safety

and operational improvements while holding aircraft to reasonable sizes and gross

weights.

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ADVANCED COMPOSITES AND ADVANCED STRUCTURES

Advanced composites coupled with various, possibly new, structural concepts

will further reduce the structural weight fraction of the airframe. The enhanced

reductions can then be used by designers to provide aircraft system improvements

beyond those available through material improvement alone.

New, higher-performing aircraft will be smaller and more productive for the

same mission. At a minimum, for example, these aircraft will takeoff and land from

the same airports or aircraft carriers, use the same gates at airports, cruise at the

same altitudes, and have the same or greater operational capability. For the same

gross weight, they will have greater range and/or operational flexibility. Through

new design with lower structural weight, they may be able to perform entirely new

missions.

Cost Issues

Every constituency (transport, fighter, rotorcraft, and general aviation) andevery government agency (NASA, Army, Air Force, Navy, and FAA) listed cost as a

major inhibiting factor to the more widespread application of advanced composites.

Early in the development of advanced composites, system “effectiveness” was prom-

ulgated as the justification for using a material that cost $100 or more per pound.

Aluminum alloys could be purchased for $1or $2 per pound.

Although significant reductions in cost have been realized, there is still an order-

of-magnitude difference in the cost of carbon-epoxy compared to aluminum. Some

consider material cost not a dominant cost factor. However, material cost is impor-

tant in commercial aircraft and a concern in military aircraft. At present, cost issues

run the gamut from materials to certification, tooling, and other facets of manufac-

turing aswell as the retraining of engineers and shop personnel whose expertise is in

metal technology.

Manufacturing costs are identified asa significant cost. This involves not only the

placement but the distribution and processingof material to optimize manufacturing

from cost considerations.

While grappling with the wide range of issues associated with costs, the commit-

tee noted that many people believe that costs play a dominant role in the selection of

the technology used in a new aircraft design. There is some concern th at system costs

have been used as an argument for inaction, both with respect to the development

of advanced composites and the development of new airplanes using composites.

If all other factors were the same, lower costs alone would encourage the fuller useof advanced composites. But these factors are not the same. The committee found

other significant technical inhibitors to the use of advanced composites, inhibitors

that can be overcome by basic research and technology development.

0 her Inhibiting Factors

Presently, designers cannot design complete composite structures with the same

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level of confidence with which a metal structure can be designed without planning for

extensive testing. The composite designer has neither the comparable metallic data

base nor methodology to address fully such structural integrity factors as strength,

longevity, damage tolerance, lightning strikes, and durability.

There is extant a very large investment in machine tools to fabricate metal

components aswell as a work force with years of experience in “cutting” metal. Thelack of an engineering data base in conjunction with an immature manufacturing

capability tips the scale toward metal technology and/or forces designers to be so

conservative that the true potential of advanced composites is not realized. Also, the

owners/operators of composite aircraft have concerns with respect to serviceability,

maintenance, and repairability because of the relatively narrow service experience

with advanced composites.

Government R&T Role

The committee recognizes the need for tough budget decisions. These decisions,

in particular, have adversely affected the levels of funding available to NASA and the

other government agencies for their aircraft structures’ advanced organic composite

research and technology development (R&T) activity. The result, in the view of

the committee,has been a genera1 sense of drifting in the NAS A program resulting,

in particular, in a loss of R&T program leadership. The committee believes the

nation cannot afford this loss. There is an important role for NASA and the other

government agencies to play in providing resources for needed R&T, in coordinating

the attack on the factors that inhibit the beneficial application of composites and

in assisting the United States in retaining a leadership role in aeronautical systems

development and sales.

Regarding the role of government in future technology development, the com-mittee agrees with earlier studies that the government has a vital role in aeronautical

R&T, including advanced composite material for aircraft structures.* This unique

role stems from the importance of aeronautics R&T in social, economic, and defense

affairs and from the diverse nature of the industry itself. Industry cannot provide

(and cannot be expected to disseminate among itself) the technology developments

needed in industry for design, development, and manufacture, and by government

user agencies (U.S. epartment of Defense and FAA) for advanced aircraft system

specification, definition, and certification.

The advanced composite material R&T addressed in this report has been identi-

fied as important to aeronautical developments through the year 2000 andbeyond.13J5 It is particularly important to the first of the three major aeronauti-

cal R&T policy areas (subsonic, supersonic, and transatmospheric) identified by the

President’s Office of Science and Technology Policy (OSTP)1~14*17in their studies

*See items 1, 9, 12, 13, 14, 15, and 17 in the bibliography listing. The following document,published after the work of this study was completed, also relates to the role of government inresearch, technology, and development: ‘National Aeronautical R&D Goals: Agenda for Achieve-ment,” Executive Office of the President, Office of Science and Technology Policy, Washington,

D.C., 1987.

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of aeronautical R&T policy. The subsonic goal ( to which most of the committee’s

comments apply) identified by OSTP notes that the United States should

Build trans-century (civil) renewal through new technology, affordable aircraft, a mod-ernized air space system, and key technology advances for 1995 readiness. This activitywill support military aircraft development and supersede foreign technology challenges.

Although the committee did not address the details of a possibile R&T program,

the committee firmly believes th at the appropriate government agencies should do

so, led by NASA. The effort should be aimed at understanding the fundamental

knowledge needed to build composite aircraft structures for the twenty-first century.

This planning, of course, must include consideration of advanced metals and metal-

composite mixes.

FINDINGS

In summary the committee has arrived at the following major findings:

Technology Maturation-Advanced organic composites need to proceed

through a technology maturation phase that includes manufacturing. The tech-

nology has reached an application plateau far below its potential height. An order-

of-magnitude increase in resources devoted to the development of basic knowledge,

requiring both analyses and experiments, is justified, in the view of the committee,

on the basis of the aircraft performance and cost gains to be realized.

National Need-The sale of aircraft is presently the major contributor to

a positive balance of payments for industrial products, but foreign competition is

becoming stronger. Looking to the year 2000, aircraft primary s tructural weight can

be reduced by some 20 to 25 percent and possibly by asmuch as 50 percent compared

to an all metal structure. Costs can also be reduced by this magnitude, providingthe United States with a competitive posture in aircraft sales against strong and

growing foreign competition.

Technology Potential-Advanced organic composites are an enabling tech-

nology for achieving the nation’s subsonic goal of ranscentury leadership in subsonic

aircraft. This is a primary technology for allowing significant reductions in structural

weight fraction.

Weight-Saving Implications-Applicat ions of advanced organic composites

have verified the predictions of lower structural weight, and the performance ad-

vantages of reduced structural weight have been demonstrated. Advanced organic

composites have been and will continue to be used to improve aircraft range and

takeoff gross weight through weight saving. A lighter structure permits the addi-

tion of fuel for greater range or airplane downsizing to achieve the same range and

payload or to allow new capability.

N e w Capability-The unique characteristics of advanced organic composites

make it possible to build new types of aircraft such as highly maneuverable, high

alti tude, vertical and short takeoff and landing vehicles and enabled the realization

of the around-the-world Voyager, which, in all probability, if constructed of metal

1.

2 .

3.

4.

5 .

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10

would not have useful range and payload. The ability of the designer to tailor

struc tural properties, for example, makes possible the design of structurally efficient

forward swept wings while avoiding serious aeroelastic problems, and to fabricate

unique structural shapes and configurations. Organic composite material may offer

an opportunity for enhancing the low observable characteristics of military aircraft.

Flight Safety-Greater flight safety can be achieved by using some of thereduction in structural weight fraction to increase current levels of structural crash-

worthiness and t o accommodate increasing amounts of avionics for providing such

capability as blind landing, collision avoidance, wind-shear warning, and fault toler-

ant control.

7 . Productivity-Greater productivity is also possible for civilian and military

aircraft. For the military, the structural weight reduction can be used to increase

payloads, whether passengers or cargo, for transport aircraft, or to allow an aircraft

to serve dual functions-air superiority and attack.

Lower-Cost Manufacturing-There is the potential, while largely unproven,

of significant cost gains through low-cost manufacturing using such techniques asfilament winding, protrusion, and hot forming, as well as integrated-structure fabri-

cation of fuselages and wings. Reduced costs here will remove an application barrier

and enhance the competitive position for US. ircraft.

Support-Issues pertaining to maintenance, serviceability, repairability, and

supportability will require continuing diligence but do not appear to be insurmount-

able. There are some nagging concerns about repair, nondestructive evaluation

techniques, and environmental effects, but the recommended R&T should help allay

and resolve these concerns and lead to an improved ability to apply composites.

10. Inhibiting Factors-A partial list of factors that inhibit the more aggressive

application of advanced organic composites, and need to be resolved, are:

6.

8.

9.

(a) a smull data base, much smaller than available for metals, e.g., there is

no document comparable to MIL Handbook 5 for composite materials due to the

difficulty of producing appropriate data. In general, the design data base must be

larger for composites due to material anisotropy and the lack of well-defined failure

theories.

(b) the relative lack of knowledge of the behavior o f mechanically fas ten ed

jo in t s ,

(c) a concern in some quarters about the lack of re liab ility of bonded jo in ts

and sandwich construction,

(d) a much less complete and poorer understanding of fracture and failuremodes and behavior under cyclic louds, especially for rotorcraft, e.g., there is no an-

alytic methodology (discipline) for composites comparable to linear elastic fracture

mechanics for metals,

(e) a lack of verified methodologies, based on the physics of filamentary com-

posite structural behavior; composite designers are not able at this this time to design

with the same degree of confidence for, longevity, damage toIerance, durability, and

other aspects of st ructural integrity including fracture as they can with metals; as

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11

an example, fracture toughness, a rigorously defined and measurable characteristic

of metals, is not well defined nor is there an agreed-upon, measurable characteristic

for advanced organic composites,

(f) high production costs requiring improved manufacturing technology,

(g) the adverse efects of lightning strikes on structural integrity, and

(h) the potential for smoke and tozicity from fires.

11. Technology Application-The technology in this study, while restricted to ad-

vanced organic composites in support of the subsonic national aeronautics goal, will

support the other national aeronautical goals, the supersonic cruiser, and the trans

atmospheric vehicle. One example, the organic composite methodologies to assess

fracture, longevity, damage tolerance, and durability will provide the foundation for

the methodologies to address the additional complexities of the high temperatures

of high supersonic and hypersonic flight. These methodologies would be generally

applicable to matrix materials other than organics and may offer attractive potential

for high-temperature structures, i.e., metal matrix and carbon-carbon.

12. Large-Scale Tests-Large-scale tests of composite structures are consideredessential to the full development of composite technology. Such tests provide impor-

ta nt information related to design, tooling, manufacturing, and testing. However,

for a given program of necessity the da ta are restricted t o selected materials and

a selected structural design and do not extrapolate easily to the broad range of

composite materials and st ruc tural configurations available to designers. Thus, to

be effective, technology development programs need to address composite built-up

structural elements as well as components.

The committee believes that the technical issues identified above can be resolved

through appropriate R&T. Cost is an issue but it is not separable from the technical

issues. The committee believes affordable aircraft will be forthcoming if its recom-mendations for R&T are implemented. A major potential barrier is an attitude in

government circles that government support is no longer necessary or justifiable.

The committee does not agree with this position.

The committee concludes that the government must consider the developmentof a new advanced organic composite R&T structures program for aircraft.

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Recommendat ions

Based upon its findings the committee offers the following recommendations

noting that the tough budget decisions made a few years ago have created a program

malaise and have seriously degraded the leadership role of NASA in the impor-

tant technology of advanced organic composites for aircraft structures. Momentum

generated by past NASA programs, such as those directed at medium primary struc-

tures, is rapidly dissipating. The committee believes it is timely and appropriate to

begin a BOLD NEW PROGRAM (BNP) characterized by the following THRUSTS,

which are discussed in more detail in Sections I and I1 of the report Supplement.

The reader is encouraged to examine the Supplement.*

THRUSTS

1. N E W S T R U C T U R A L C O N C E P T S : The BNP should foster full recogni-

tion that the basic components of advanced organic composites are filaments and

matrix, i.e., “strings” and “glue.” A new way of thinking needs to be promulgated to

overcome 40 years of devotion to design concepts that may be appropriate only for

isotropic metallic materials. It has been said with much accuracy that many, if not

most, of the present composite applications are “black aluminum”; the metal ma-

terial in a metal design has merely been replaced with black filamentary composite

material. More innovative design and manufacturing concepts that fully utilize theinherent characteristics of composites must be pursued. University programs could

be helpful here. (Pages 23,24,26, 29)

2. MANUFACTURING: The BNP should encourage new manufacturing

methods that will exploit the filament and matrix nature of composite materials

*Some of the committee’s views relevant to these THRUSTS and the following RECOMMEN-DATIONS are on the pages of the Supplement noted after each summary statement.

12

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13

and reduce production costs. Structura l concepts should be integrated with manu-

facturing. There is a tremendous investment in metal shaping and fabricating tools,

but progress in the application of advanced composites has been and will continue

to be impeded if the tooling for metals continues to be used for filamentary com-

posites. “Free” thinking, leading to new and improved concepts, will be discouraged

if the designer thinks in such terms as five-axis milling machines, drill presses, andconventional tooling concepts. (Pages 25 , 26 , 29 )

3. CRITICAL EXPERIMENTS: Experiments (of sufficient scale) are the

linchpins to a better and sufficient understanding of the fundamental issues of frac-

ture, longevity, damage tolerance, durability, and other issues of structural strength

and integrity. Critical work should be identified and supported. (Pages 26,29)

4. DESIGN M ETH ODOLOGY: The development of analytical methods that

blend theory and empirical and experimental data , and permit extrapolation of da ta

from the laboratory to full-scale design, is very important. Analytical methods for

failure analyses are needed for designers to assess properly the s tructural margins

of safety. It is important to recognize that large finite-element programs that make

use of supercomputers will spew out reams of useless answers if the failure theories

and analytical methods are in error. The design methodology is only as good as the

experimental data base upon which it is structured and hence this analytical thrust

must be closely coordinated with and depend on experiments for proof. (Pages 24 ,

25, 26, 29)

5. DATA BASES: The term “data bases” as used herein relates t o material

and structural matters required to reduce the risks of new composite structure de-

signs to levels acceptable to designers and chief engineers. Data pertinent to such

matters asmaterial properties (ranging from tensile ultimate strength to behavior a t

moderate and high temperatures to moisture absorption), methods of testing, com-

pressive behavior of laminates, and bonded-joint design have to be addressed. Well-organized and well-documented data bases should be published and disseminated to

appropriate government, industry, and academic organizations. It is recognized that

the development of material da ta bases will be a more difficult, drawn-out process

than that forother technical matters due to the dynamics ofmaterial development.

This difficult matter should be explored with industry to identify what should be

pursued. (Pages 23, 26, 29, 36)

6. EDUCATION: Generations of young engineers are needed whose baseline

knowledge is orthotropic rather than isotropic, heterogeneous rather than homoge-

neous, and who deep down in their pysches regard metals as a special case of fila-

mentary composites. The BNP should address resources to the engineering schools

to help achieve these goals. (Pages 25, 26, 29)

RECOMMENDATIONS

Based on the preceding observations and committee deliberations, and Sections

I and I1of the report Supplement, the committee RECOMMENDS the following:

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1. The government, through NASA, DOD, and FAA, should establish a BOLD

NEW PROGRAM for advanced organic composites research and technology devel-

opment (R&T). The committee believes an order-of-magnitude increase in funding

is justifiable on the basis of the expected returns. (Pages 36,37)

2. The objectives of the BOLD NEW PROGRAM should be to enlarge the

technology data base and to enhance the opportunities for early application of thetechnology. (Pages 23,29,38)

3. The BOLD NEW PROGRAM should be innovative and visionary, and the

R&T effort should provide the government and industry with the capability to

capitalize on the potential of advanced organic composite materials. (Pages 23, 25,

4. The BOLD NEW PROGRAM, in addition to basic R&T, should be directed

at cost reduction from material to design through construction and testing; the pro-

gram should expand the related da ta bases, include necessary large-scale technology

validation activity, and appropriately support related academic activity. (Pages 23,

5 . NASA, DOD, and FAA should jointly define and implement the program

with inputs from industry and the universities and consider joint ventures for large-

scale expensive projects. (Pages 25,26, 9,31, 34,36,37,41)

40)

37)

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Bibliography

1. Office of Science and Technology Policy. 1987. National Aeronautical R&D

Goals, Agenda for Achievement. Washington, D.C.: Executive Office of the Presi-

dent.

2. Office of Technology Assessment. 1986. New Structural Materials Technolo-

gy-Opportunities for the Use of Advanced Ceramics and Composites. Technical

memorandum (September), Washington, D.C.

3. U.S. Air Force. 1986. Defense Advanced Research Projects Agency studies

new materials to boost aircraft performance. Aviation Week and Space Technology

(June 23):167.

4. Johnson, Warren P. 1986. Materials and process requirements for advanced

aerospace systems-near term and far term. Paper presented at Thirty-first Inter-

national SAMPE Symposium, April 7-10, 1986.

5. Scheer, Maj. Christopher, and James W. Jones. 1986. Project Forecast 11.Newsreview 30(4):(March 7).

6. National Research Council. 1986. N e t Shape Technology in Aerospace Struc-

tures. Committee on Isolation of Faults in Air Force Weapons and Support Systems.

Washington, D.C.: National Academy Press.

7. Sweetman, William. 1986. Stealth aircraft, secrets of future airpower. Osce-

ola, W is.:Motorbooks International.

8. Plaice, Ellis. 1986. Airframe manufacturing using non-metals. World Aero-

space Profile, page 51.9. Maggin, Bernard. 1985. Advanced aeronautical technology and its impact

on the competitive position of the U.S. Paper presented at SAE Aerotech '85, Long

Beach, California, October 14-18.

10. Keyworth 11,Dr. G. A. 1985. High speed aerodynamics. Testimony before the

Subcommittee on Transportation, Aviation, and Materials, Committee on Science

and Technology, U.S. House of Representatives, July 24.

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11. Proceedings of the Seventh Conference on Fibrous Composites in Structural

Design. AF WAL-TR-85-3094. Air Force Wright Aeronautical Laboratories, Wright-

Patterson Air Force Base, Ohio, June 1985.

12. National Research Council. 1985. The Competitive Status of the US.Civil

Aviation Manufacturing Industry. Committee on Technology and International Eco-

nomic and Trade Issues. Washington, D.C.: National Academy Press.

13. National Research Council. 1985. Aeronautical Technology 2000: A Projec-

tion of Advanced Vehicle Concepts. Panel on Vehicle Applications, Aeronautics and

Space Engineering Board. Washington, D.C.: National Academy Press.

14. Officeof Science and Technology Policy. 1985. National Areonautical R&D

Goals: Technology for America’s Future. Washington, D.C.: Executive Office of the

President.

15. National Research Council. 1984. Aeronautics Technology Possibilities for

2000: Report of a Workshop. Aeronautics and Space Engineering Board. Washing-

ton, D.C.: National Academy Press.

16. Wittlein, Gil, Max Gamon, and Dan Skycoff. 1982. Transport Aircraft CrashDynamics. FAA Report DOT/FAA/CT-82/69 (March). NASA Contractor Report

165851. Burbank, Calif.: Lockheed-Calif. Co.

17. Office of Science and Technology Policy. 1982. Aeronautical Research and

Technology Policy. Washington, D.C.: Executive Office of the President.

18. Kuperman, M. H., and R. G. Wilson. 1977. Today’s non-metallic composite

airframe structure-an airline assessment. Paper presented at the Ninth National

SAMPE Technical Conference, Atlanta, Georgia, October 1972.

19. Leslie, James C. Properties and Performance Requirements. In Advanced

Thermoset Composites, James M. Margolis, ed. New York: Van Nostrand Reinhold.

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Supplement:

Summary of Committee Study

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Section I

Program Assessment

In its review of advanced organic composite technology the committee considered

(a) their potential advantages, (b) inhibiting factors or barriers to their application,

(c) technical issues that need to be resolved to help accelerate their application, and

(d) possible actions the government could take (through the National Aeronautics

and Space Administration [NASA],U.S.Department of Defense [DOD],and Federal

The committee’s views on these matters are summarized in this Supplement

(which addresses aircraft manufacturers and airlines, composite material manufac-

turers, and government agencies) based on the committee’s review of the material

presented to i t and its own deliberations.

Aviation Administration [FAA]).

AIRCRAFT APPLICATIONS

The committee used four classes of aircraft-large transports (and airlines as

users), rotorcraft, high-performance aircraft, and general aviation-for its assess-

ments of potential advantages, inhibiting factors, technology needs, and possible

government actions. Following is a summary of these assessments.

Potential Advantages

Advanced organic composites can, if the technology is fully developed, provide

appreciable advantages for all classes of new, advanced aircraft. Some of the moreimportant advantages are listed in Table S-1-1. These range from reduced costs for

design, manufacturing, and operation of the aircraft to aerodynamic and structural

tailoring to improved crashworthiness and life. The importance of each varies with

class of aircraft.

The subjects of reduced structural weight, increased aircraft productivity, and

reduced costs are fundamental drivers of research and technology for all classes of

19

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T A B L E S-1-1 P o t e n t i a l A d v a n t a g e s

S u b j e c t

Assessment

L a r g e H i g h -T r a n s p o rt s P e r f o r m a n c e G e n e r a l& A i r li n e s R o t o r c r a f t A i r c r a f t A v i a t i o n

R e d u c e d s t r u c t u r a l w e i g htI n c re a se d a i r c r a f t p r o d u c -

R e d u c e d c o s ts : d e s ig n , d e -t i v i t y

v e l o p m e n t , m a n u f a c t u r i n g ,a n d o p e r a t io n s

t a i l o r in g

r e d u c e d f a t i g u e

A e r o d y n a m i c a n d s t r u c tu r a l

I n c re a s ed s t i f f n e s s a n d

I m p r o v e d p e r f o r m a n c eR e d u c e d c o rr o s io n , m a i n -

t e n an c e , a n d r e p a i rI m p r o v e d c r a s h w o r th i n e s sD a m a g e r e d u c t i o nL o n g l i f e

1

1

1

2

22

2222

1

1

1

1

1

1

1

122

11

1

1

1

1

1222

11

1

2

22

2222

K E Y : 1 - -V e ry i m p o r t a n t

2 - - I m p o r t a n t3 4 i g n i f i c a n t

aircraft. With advanced organic composites, primary st ruc tural weight reductions

of 20 to 25 percent are probable and up to 50 percent potentially possible, compared

to a metal structure. This can be translated into various combinations of longer

range, reduced fuel consumption, or larger payloads.

Reductions in cost for design, development, and manufacturing will help broaden

the market for individual aircraft and improve their competitive posit ion. Reduced

operational and life-cycle costs are possible because of the potential for reducedinitial and operational costs through the integration of design and manufacturing,

the manufacture and assembly of fewer parts, the automation of manufacturing, the

reduction of labor requirements, and the increase in productivity per unit of cost.

Composites produce smooth, finished surfaces and permit variable contours to

maximize aerodynamic efficiency. They can be designed precisely to net-shape with

fiber orientation to give the desired stiffness and achieve maximum structural ef-

ficiency. Structural efficiency is enhanced further by the reduced susceptibility to

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2 1

fatigue of composite structures. These factors combine to improve aircraft perfor-

mance, and they synergistically interact with other factors th at increase operational

efficiency and, thus, productivity.

The matters of tailoring stiffness, reducing fatigue, and lowering structural

weight are relatively more important for rotorcraft because of their severe oper-

ating environment and higher weight empty fraction.Because composites are stiffer than metals, do not corrode, and experience less

fatigue, they should require less repair and maintenance than metal structures. This

basic stiffness advantage is important to all of the aircraft classes. For rotorcraft,

additional potential advantages are reduced vibration and cyclic loads. For high-

performance aircraft a significant potential advantage is greater capability to sustain

repeated high-stress maneuvering.

Although a conventional composite structure has relatively poor crashworthiness

due to its lack of inherent plasticity and residual strength following yield, current

Army and FAA research indicates that, when properly designed to enhance crash-

worthiness, a composite structure can have a higher specific energy absorption than

a metal structure. This represents a fertile area for additional research if the full

benefit of composite structures is to be realized. The potential for improved crash-

worthiness, at a reduced weight penalty, is important for both civil and military

rotorcraft.

Inhibiting Factors

Use of advanced organic composites has been limited because of the inhibiting

factors listed in Table S-1-2. Thus, the potential advantages addressed above have

not been fully exercised.

Among the major inhibiting factors for all aircraft classes are the high costs ofdesign, development (including certification), and production of advanced organic

composite structures. Design and development costs are pervasive. They involve

such matters as (a) the lack of technology data bases from design to test to certifica-

tion to manufacturing, (b) limited understanding of failure mechanisms and related

analytical methods for predicting and designing to avoid failure, (c ) the inability to

certificate (acceptance for military aircraft) with assurance, (d) low tolerance to ac-

cidental, natural, and battle damage, (e) the need for nondestructive inspection and

testing techniques, ( f ) difficulty in making repairs in the field, and (g) the low-stress

limits of present advanced organic composite materials.

Certification deserves special comment. It is a cost item because of the time

and complexity of a process that in the end has not had high success. This has

resulted in an understandable reluctance on the part of designers and manufacturers

to apply composites aggressively, particularly in civil aircraft. Technical uncertain-

ties associated with design and development, and the certification process itself,

are inhibitors. The certification agencies (FAA and DOD) also have difficulties in

identifying appropriate tests and processes for validating safety, performance, and

life characteristics and in assessing test data. The difficulties experienced by the

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T A B L E S-1 -2 I n h i b i t i n g F a c t o r s

S u b j e c t

Assessmen tL a r g e H i g h -T r a n s p o r t s P e r f o r m a n c e G e n e r a l

& A i r li n e s R o t o r c r a f t A i r c r a f t A v i a t i o n

Hi g h co s t s- -d es ig n , de-

L a c k o f t e c h n o lo g i c a l d a t av e l op m e n t , a n d p r o d u c t i o n

b ase

m e c h a n i s m sU n d e r s t a n d in g f a i l u r e

L o w t o l e ra n c e t o d a m a g eI n a d e q u a t e n o n d e s t r u c t i v e

C e r t i f i c a ti o n d i f f i c u l t yD i f f i c u l t y o f d a m a g e re p a

L a c k o f d e s i g n e x p e r i e n c e

C o s tl y m a i n t e n a n c e a n d

H i g h a c o u s t i c r e s p o n s eL i m i t e d m a n u f a c t u r i n g

t e s t i n g

i n f i e l d

e d u c a t i o n

r e p a i r

c a p a b i l i t y

I

I n c o n s i s t e n t m a n u f a c t u r i n g

Lo w-s t r es s l imi t sBr i t t l en ess o f ma t r i cesA d v e r s e e f f e c t s o f e n v i r o n -

M a t e r i a l c o s tA b i l i t y t o d e s i g n t h i c k - w a l l

E r o s i o n of r o t o r b l a d e sL o w t o l e r a n c e f o r h i g h

q u a l i t y

m e n t

c o m p o n e n t s

t e m p e r a t u r e

1

1

11

1

1

1

2

22

2

223

32

33

3

1

1

11

1

1

1

2

23

2

212

33

1

1

3

1

1

11

1

1

12

23

3

21

1

33

23

1

1

1

11

1

1

2

1

22

2

333

32

33

3

K E Y : 1 - -V e r y i m p o r t a n t2 - -1 mp o r t an t3 - -S ig n i f i can t

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certification agencies are exacerbated by the lack of standardized definitions and

test procedures for composites.

The inability to make a full commitment to composites is in part due to the

lack of advanced production techniques, procedures, and automation. The inability

to handle design, development, and production factors expeditiously raises costs

and reduces product quality and performance. This, in turn, will adversely affectthe scope and ra te of technology development. Production (Le., manufacturing) is

inhibited by limited capability and capacity, high tooling costs, and inconsistent

quality. The ratings for these factors range from important to significant depending

on the class of aircraft (Table S-1-2).

Factors such as low-stress limits, brittleness of matrices, and environment (Table

S-1-2) affect all aircraft classes and vary in importance with class. The ability to

design (and tes t) thick-walled components is very important to rotorcraft. Such

components are used extensively in rotors and major structures, and are expected

to find their way into drive trains. Also important in rotorcraft design is avoidance

of rotor-blade erosion by sand and dust, rain and hail. A unique concern for high-speed, high-performance aircraft is the low structural tolerance of advanced organic

composites to high temperatures.

Costly repair and maintenance and lack of design experience and education are

considered universally important inhibitors. For general aviation, experience and

education are very important and of special concern because these manufacturers

have limited production facilities and staffs, and find it difficult to compete with the

large firms for trained personnel.

Comments specifically pertinent to airline operations are contained in Appendix

B, special correspondence from the Air Transport Association of America.

Technology Needs

To gain the potential advantages of composites, the inhibiting factors must

be reduced or removed. The needs, among a broad spectrum considered most

significant, are noted in Table S-1-3. They include reduced costs, concepts and

design innovation, and data bases, among other items.

Costs There is no question tha t costs must be reduced. Much of the costs are asso-

ciated with manufacturing (tooling, processes, and labor), some with development

testing and certification, some with materials (which will become a larger factor withexpanded use of composites in a given design), and some with design.

New Concepts and Design Innovation The full benefits of composites will not be

realized until designs (and manufacturing processes) take advantage of the unique

characteristics of composites and composite structures are not designed and built like

metal structures. This requires new design and manufacturing concepts; it requires

innovation.

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TA BL E S-1 -3 Needs

AssessmentL a r g e H i g h -T r a n s p o r t s P e r f o r m a n c e G e n e r a l& A i r li n es R o t o r c r a f t A i r c r a f t A v i a t i o nub jec t

R e d u c e c o s tsN e w c o n ce p t s a n d d e s ig n

i n n o v a t i o nT e c h n i c a l d a t a b a s esF a i l u r e m o d e a n a l y s i s / u n d e r -

D e si gn a n d m a n u f a c t u r i n g

S i m p l i f y a n d a c c e l e r a te

E d u c a t io n a n d t r a i n in gE a s y r e p a i r a n d f i e l d r e -

A d v a n c e d c o m p o s it e s p r o g r a mH i g h - t e m p e r a t u r e , l o n g - l i f e

H o n e y co m b a n d s a n d w i ch

s t a n d i n g

i n t e g r a t i o n

c e r t i f i c a t i o n / a c c e p t a n c e

p a i r a b i l i t y

p rocessab le sys tems

sys tems

1 1 1 1

11

1

111

11

1 1 1 1

11 1

12

12

12

11

23

23

22

2

1

3 3 1 3

33 3

K E Y : 1 - -V e ry i m p o r t a n t2 - - I m p o r t a n t3 - -S ign i f i c an t

Data Bases The large manufacturers are building data bases for design, testing,

and certification. These da ta bases are not universal nor are they available to other

manufacturers. The proliferation of new basic materials and composites, and designs

and processes make the maintenance of data bases complex and expensive. Some

semblance of order and standardization is required if the time, complexity, and cost

of design and testing are to be reduced and certification is to be approached with

confidence.

Failure M o d e Analysis and Understanding If designs are t o be sound and certifiable,

failure and its progression and an understanding of how to design to avoid failure

under severe operating conditions must be predictable. Analytical tools-theoretical

and/or empirical-that provide this capability are needed to assist in design and

testing for safe, long-life composite structures.

Design and Manufacturing Integration To capitalize fully on composites, innovation

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in design must be integrated with innovation in manufacturing. The very process-

ing of composites affects the characteristics of the material and the finished part .

The activities are interdependent not independent. Automated manufacturing will

reduce production costs and improve quality control.

Simp lify and Accelerate Certificatio n There are two parties t o certification-industryand government, i.e., the producer and the certificator/acceptor. The producer

needs to know what to design for and how to design and test for certification. The

certification agent needs to specify requirements and procedures that will satisfy

guardianship of the public interest. Data bases on related matters will help. There

is a need for a high level of confidence in the ability t o certify a new composite

aircraft design including the realization of reduced certification process time and

cost. Particular attention to simplification and acceleration of the process is needed

and warranted.

Education and Rainin g Most people involved in composites today were not trained

in this specialty field. Expanded development and application of composites willrequire an enlargement of the cadre of professionals and technicians in the field. The

problem is specialized training in this relatively new field. Needed is cooperative

effort among industry, government, and universities on both near- and long-term

educational matters.

Advanced Com posites Program An advanced composite rotorcraft program that ad-

dresses generic technology development (noted in the discussion on inhibiting factors

development effort must include validation of the generic technology at reasonable

system scales and give attention to new, innovative rotorcraft concepts. Relatedwork for transport and the other classes of aircraft, with a focus on generic primary

structures (fuselages and wings), is considered by the committee to be an impor-

tant , integral part of the technology development effort for helping U.S.aircraft

manufacturers maintain a competitive edge in world markets.

pertinent to rotorcraft) would significantly improve these aircraft. The technology

Ease of Repair and Field Repairability Important to all aircraft classes is ease of repair

at the maintenance base and in the field from time, cost, and tooling considerations.

Owners and operators need techniques and tools that allow simple and inexpensive

repairs in the field. This is especially important for military and airline operations.

Service disruption results in loss of mission or revenue.

High-Temperature, Long-Life Systems Composite systems that can tolerate high

temperatures, have long life, and are readily processed into components and struc-

tural elements are critical to the development of future high-speed and high-perfor-

mance military aircraft. These aircraft will operate at high-supersonic (in the future

possibly at hypersonic) speeds for extended periods of time. Organic composite ma-

terials and structural designs are needed tha t can withstand temperatures to about

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550°F.But, of course, much higher temperatures must also be dealt with for exterior

structures and propulsion system elements.

Honeycomb and Sandwich Systems Although there has been a movement away from

honeycomb and sandwich composite structures due to poor past performance un-

der conditions of high humidity and widely varying temperatures, they warrantre-examination because these systems are efficient and relatively inexpensive. Hon-

eycomb and sandwich systems can be very important to general aviation and have

significant value for the other aircraft classes.

Possible Government Action

Table $1-4 lists some of the more important actions that government agencies

could take, related to aircraft design, manufacturing, and testing, to help further

the application of advanced organic composites. The government agencies can: (a)

build technology confidence, (b) continue support of basic research, (c) support, se-lectively, the development of data bases, (d) support development of new structural

concepts and innovative structural designs including manufacturing processes, and

where appropriate, large-scale (including flight) integrated system concept testingfor technology development, (e) develop fatigue and failure mechanism analyses,

(f) identify and pursue activity to reduce the time, cost, and uncertainties of cer-

tification of composite aircraft structures, (g) support development of advanced

manufacturing techniques and processes, and (h) support fellowships and other ed-

ucational endeavors to help improve the cadre of professional and support people in

the field of composite aircraft structure design, development, manufacture, testing,

and operation.

Other subjects warranting government support, because they are important or

of significant value, involve the exploration of the potential for application of new

and innovative composite structures, the development of technology pertinent to

damage-tolerant design, and the definition and development of an advanced com-

posite aircraft technology program encompassing large-scale validation of analyses

and small-scale experiments.

MATERIAL MANUFACTURERS

Table S-1-5 ummarizes the observations of the committee with regard to three

classes of materials having special interest to aircraft designers and manufactur-

ers: (1)epoxy resin pre-impregnated fiber (prepreg), (2)bismaleimides/polyimides

(BMI/PI)or higher-temperature applications, and (3) thermoplastics for manufac-

turing advantages.


Epoxy resin prepreg has the advantages of lower-cost manufacturing, existing

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T A B L E S-1-4 P o s si b le G o v e r n m e n t A c t i o n

Sub j ec t

Asses sm en tL a r g e H i g h -T r a n s p o r ts P e r f o r m a n c e G e n e r a l

& A i r li n e s R o t o r c r a f t A i r c r a f t A v i a ti o n

B u i l d t e c h n i c a l c o n f i d e n c eS u p p o r t t e c h n i c a l d a t a - b a s e

Suppor t ba s i c r e s ea r chS u p p o r t n e w c o n c e p t a n d i n -

n o v a t io n d e s ig n a n d m a n -u f a c t u r i n g

D e v e lo p f a t i g u e a n d f a i l -u r e m e c h a n i s m a n a l y s es

R e d u c e t i m e a n d c o s t- -c e r-t i f i c a t i o n / a c c e p t a n c eS u p p o r t f e l l o w s h i p sE x p l o r e p o t e n t i a l a p p l i -

D e v e l o p a d v a n c e d c o m p o s i t e

d e v e l o p m e n t

c a t i o n s

( f l i g h t ) a i r c r a f tt e c h n o l o g y p r o g r a m

r e d u c t i o n

t h e rm o p l a s ti c s m a n u f a c -

t u r e

des i gn t echno l ogy

A d d r es s m a n u f a c t u r i n g c o s t

D e v e l o p te c h n o lo g y f o r

D e v e lo p d a m a g e t o l e r a n t

1

11

1

1

11

1

2

2

2

3

1

1

1

1

1

11

2

2

2

2

1

1

11

1

1

11

2

2

2

1

3

1

11

1

1

11

2

3

2

3

3

KEY: 1 - -V e r y i m p o r t a n t2 - - I m p o r t a n t3- -Signi f i ca nt

da ta bases (within a few companies), experience, and available facilities. However,

there is significant room for technical advancement in each area.

BMI/PI composites can withstand the moderately high temperatures (up to

about 550°F) associated with moderate supersonic flight speeds. Like epoxy, to

some degree, the kinds of tools needed for manufacturing are in-hand, but da ta

bases and experience are less and costs are higher than for epoxy.

Thermoplastics have high potential. They can handle higher temperatures than

the other organic composites noted and possess higher toughness. There is also a

potential for lower-cost,uniform manufacturing.

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T A B L E S-1-5 S u m m a r y O b s e r v at i o n s- - M a t e r ia l s

P o t e n t i a l I n h i b i t i n gA d v a n t a g e s F a c t o r s N e ed s

Possib le

G o v e r n m e n tAc t ions

E v o x vL o w e r c o s ts M o i s t u r e d a m a g e R a i s e t o u g h n e ss D e v e l o pE x i s t i n g L o w t o u g h n e ss a n d t e m p e r a t u r e m e a s u r e m e n t

d a t a b a se a n d e as e of a n d e v a l u a t io nE x p e r i e n c e d a m a g e t e c h n iq u e s a n dE x i s t i n g S u p p o r t a b i l i t y processes

f a c i l i t i e s

Bismaleimides/volvimidesH i g h H i g h c o st

t e m p e r a t u r eI m p r o v e

processingD e v e l o p

m e a s u r e m e n ta n d e v a l u a t io nt e c h n iq u e s a n dprocesses

T h e r m o v l a s t i c sG r e a t e r H i g h c o st I m p r o v e D e v e l o p

rep rod uc ib i l i ty Ava i l ab i l i ty ma nu f a c tu r i n g m e a s u r e m e n tE a se o f r e p a i r N e e d f o r h i gh m e t h od s a n d e v a l u a t i o nH i g h e r t e m p e r a t u r e a n d I n cr e as e t e c h ni q u e s a n d

Highe r p rocess ingt e m p e r a t u r e p r e s s u re f o r d a t a b a s e p ro c es s es

toughness

Inhibiting Factors

Epoxy systems are subject to strength reduction, i.e., environmental damage,

due to moisture ingestion if detailed attention is not given to design. The materials

have low toughness and are relatively easily damaged. This can lead to problems con-

cerning damage detection, knowledge of the extent of damage and failure potential,and when and how to repair.

BMI/PI materials are relatively expensive. They are inherently brittle and

possess low toughness. These factors lead to the same class of supportability issues

that epoxies have.

Thermoplastics have had relatively little application in aircraft. Their costs are

high, they are relatively unavailable, and they require high pressure and temperature

for forming components.

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Needs

Epoxy’s major drivers, from material considerations, are increased toughness

and higher usable temperatures than are available today. However, considerable

progress in toughness has been achieved since 1985.

For BMI/PI, one of the more important needs is to improve the ability t o process

these materials with consistency and low cost.

Possible Government Action

In the area of materials the committee believes that the government can be

of most help through at tention to the development of s tandards of measurement,

evaluation techniques, and basic material production processes. Although industry

can develop materials, it is not in the best, most unbiased, position to develop and

set standards for the measurement and evaluation of materials. It is the view of the

committee that the detailed development of new materials, manufacturing processes,

and applications can be left essentially to the materials industry in concert with theaircraft designers and manufacturers. However, in the area of basic understanding

of chemical and mechanical processes, government research and technology devel-

opment support would be very useful in accelerating fundamental underst anding,

leading to industrial development and application.

GOVERNMENT AGENCIES

The views of government representatives on important technology development

needs are summarized in Table S-1-6. The technology development needs noted for

the Army relate to rotorcraft; the Navy and Air Force needs relate principally to

high-performance aircraft; the FAA to transport, general aviation, and rotory-wing

aircraft; and NASA to generic research and technology. Observations common to all

aircraft classes are summarized in Table S-1-7.The data in Tables S-1-6 and S-1-7 reinforce the earlier industry discussions of

needs, potential advantages, inhibiting factors, and needs.


The government agencies see common advantages and benefits associated with

advancing the st ate of technology of advanced organic composites. These bene-

fits relate to broader design, operational, and mission flexibility and thus greaterperformance and/or productivity. They see the potential for reducing the costs of

composite structures through enhanced technology, advanced designs, and greater

application of composites. The committee agrees with the government agency rep-

resentatives’ belief that successful pursuit of these advantages will help maintain

U.S. competitiveness and preserve U.S. jobs in aircraft development and produc-

tion programs. Thermoplastics have interesting potentials but there is relatively

little experience with applications. Application would be enhanced with improved

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T A B L E S-1-6 I n d i v i d u a l G o v e r n m e n t A g en c y V i e w s o n A d v a n c e d O r g a n i cC o m p o s i te T e c h n o l o g y D e v e l o p m e n t N e e d s

U.S. A r m vC o m p o s i te s f o r r o t o r b l a d e s t h a t

w i t h s ta n d r a i n a n d s a n dD e si gn c r i t e ri a a n d s t a n d a r d s f o r

d a m a ge , d u r a b i l i ty , a n d f a t i g u eD e s ig n f o r d a m a g e t o le r a n c e ,

d u r a b i l i t y , a n d c r a s h w o r t h i n e ssM e t ho d s ( s t a n d a r d s ) f o r h a n d l i n g

f a t i g u e i n a u n i f o r m a n d c o n s is te n tm a n n e r

R e a l i st i c q u a l i f i c a t i o n p r o c e d u r e s

U.S. N a v yN e w m a t er ia l s a n d m a t e r i a l f o r m s t o

m e e t m o r e s e v e r e d e s i g n c o n d i t i o n s ,i.e., wo v en co mp o s i t e s a n d n ew res insy s t ems

S y st em s f o r b e t t e r i m p a c t a n d d a m a g er e s i st a n c e , s u r v i v a b i l i t y , l o wc o s t, s u p p o r t a b i l i t y , c r a s h w o r t h i n e s s ,f a t i g u e l i fe , d u r a b i l it y , a n dm a i n t a i n a b i l i t y i n c l u d i n g a n a l y t i c a ltoo ls

P o s t b u c k l i n g a n a l y s i s m e t h o d o l o g yC e r t i f i c a t i o n p ro c e d u r e d e f i n i t i o nL o w - w e i g h t d e s i g nI ss ue a r e as : a i r f r a m e s a n d s t r u c t u r a l

i n t e g r i t y , l a n d i n g g e a r s , l o a d a n dl i f e m a n a g e m e n t , s u p p o r t a b i l i t y , a n de l e c t r o m a g n e t i c c o m p a t i b i l i t y

U.S. A i r F o r c eR e s e a r c h a n d d e v e lo p m e n t : t h e r m o -

s e ts - -n e w p o l y m e r c o n c e p t s a n d r e s i nch arac t e r i za t i o n , p ro cess in g sc i en ce ,o r d e r e d p o ly m e r f i b e r a n d f i l m ,mo lecu l a r co mp o s i t e s , o p to -e l ec t ro n i cm a t e r i a l s

p o s t f a i l u r e a n a l y s i s , p a i n tr e m o v a l, a n d t h e r m o p l a s ti c s u p p o r t

M a n u f a c t u r i n g t e c h n o lo g y a n d s c ie n ce :r e g a r d in g c o m p u t e r - a i d ed c u r e o fco mp lex sh ap es , i n t eg ra t ed co mp o s i t e sc e n t e r , l a r g e c o m p o s it e a i r c r a f t

T h e r m o p l a s t ic a n d o r g a n i c m a t er i a ls f o rp ro p u l s io n sy s t ems

S u p p o r t a b i l i ty : f i e l d r e p a i r m a t e r i a ls ,

F e d e r a l A v i a t i o n A d m i n i s t r a t i o nD e t e c t i o n o f u n d e r s t r e n g t h b o n d s (a l l

F a i l u r e a n a l y s is m e t h o d o lo g yS t a n d a r d s f o r m a t e r ia l p r o p e r t y t e st in gC o s t - e f f e c t i v e f i n i t e e l e m e n t a n a l y s i s

t e c h n i q u e s f o r c o m p le x -l oa d t r a n s f e ra r e a s

c h a r a c t e r i s t i c s o f m a t e r i a l s

classes)

F l a m m a b i l i ty , t o x ic i ty , a n d s m o k e

D a m a g e g r o w t h a n a l y s i sR e p e a t e d - l o a d r e s p o n s eS t a t i s t i c a l a n a l y s e s t o a l l o w r e d u c t i o n

o f m e c h a n i c a l t e s t i n gF u l l -s c a l e c o m p o n e n t r e s p o n s e v e rs u s

c o u p o n r e sp o n se a n d d a t a s c a t te rC r a s h w o r t h i n e s sL i g h t n i n g - s t r i k e b e h a v i o r

N a t i o n a l A e r o n a u t i c s a n d SPaceA d m i n i s t r a t i o nS y s te m s c h a r a c t e r i z a t i o n : m e c h a n i c a l

p r o p e r t i e s , d a m a g e t o l e r a n c e ,m i c r o m e c h a n i c s / f a i l u r e , a n de n v i r o n m e n t a l e f f e c t s

S t r u c t u r a l c o n c e p ts , e f f i c i e n c y , a n dt a i l o r i n g

G r a d i e n t s , d i s c o n t i n u i t i e s , c u t o u t s ,a n d d a m a g e

P o s tb u c k li n g a n d n o n l i n e a r e f f e c t sa n d a n a ly s e s

L o c a l a n d g l o b al s t r u c t u r a l a n a l y s e si n c l u d i n g f a i l u r e m e c h a ni sm s a n da n a l y s e s

S u b s c a l e w i n g - b o x a n d f u s e l a g e - s h e l lm o d e l i n g

F i l am e n t - w o u n d s t r u c t u r e sT h e r m o p l a s t i c s

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T A B L E S-1-7 S u m m a r y o f G o v e r n m e n t A g en c y V i ew s o n A d v a n c e d O r g a n i cC o m p o s it e T e c h n o l o g y D e v e l o p m e n t F a c t o rs

P o e n i a l

A d v a n t a g e s

I n h i b i t i n g

F a c t o r s

N e e d s a n d P o s si b le

G o v e r n m e n t A c ti o n

R e d u c e d s t r u c t u r a lw e i g h t a n d i n c re a s e ds t i f f n e ss

A e r o s t r u c t u r a l

t a i l o r i ngD e s i g n f l e x i b i l i t yI n cr e as e d a i r c r a f t

p e r f o r m a n c e a n d / o rp r o d u c t i v i t y

F a t i g u e r e s is t a n ceNo co r r os i onL o n g e r l i f eR e d u c e d p a r t c o u n t

a n d m a n u f a c t u r in gcosts

costsR e d u c e d l if e - c yc l e

C o m p e t i t i v e e d g ea n d j ob s

Cos t s ; des ign , devel -o p m e n t , m a n u f a c t u r e ,c e r t i f i c a t i o n , a n dm a i n t e n a n c e a n d r e p a ir

D a t a b a s e f o r d e s i g na n d t es t

M a n u f ac u r i ngt e c h n i q u e s a n dc a p a b i l i t y

L i m i t e d e x p e r i e n c ea n d t r a in e dpe r sonne l

I m p a c t d a m a g esus cep t ib i l i ty , i .e .,l o w d a m a g e t o l e ra n c ea n d u n d e r s t a n d in gf a i l u r e m e c h a ni sm s

i n v a s i v e t e s t a n di nspec t i on m e t hods

c e r t i f i c a t e

N o n d e s t ru c t iv e a n d n o n -

A b i l i t y t o

Cos t r educ t i on ;d e s i g n , m a n u f a c -t u r e , t e s t , andc e r t i f i c a t i o n

D a t a b a s e s f o rd e s i g n a n d t e s t

D e s i g n a n dm a n u f a c t u r ei n n o v a t i o n

N e w c o n ce p ts f o rs t r u c t u r a l d e s ig na n d m a n u f a c t u re

m a n u f a c t u r ei n t eg r a t i on

C e r t i f i c a t i o n ;s i m p l i fy a n dacce l e r a t e

Bu i l d t e chno l ogyc o n f i d e n c e

Large-sca le sys tems;a d v a n c e d c o m p o si te sa i r f r a m e p r o g ra m

i n c r e a s e a t t e n t i o n

p r o f e s s i o n a l a n dt e c h n i c a l s u p p o r t

D e s i g n a n d

The r m op l a s t i c s ;

E d u c a t i o n ;

manufacturing technology and enlargement of design and development da ta bases.

Particular attention needs to be given to the development of low-cost manufacturing

processes.

Inhibiting Factors

Government agency representatives view inhibiting factors as relating t o high

costs; limited design, development, and testing data bases; integration of design

and manufacturing; certification; and the lack of appropriately trained engineering

personnel and technicians. These are the same factors considered important by the

designers and manufacturers, and by the committee.

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Needs and Possible Government Action

It is the view of the committee that the government can play a significant role

in gaining the advanced organic composite benefits that have been identified in this

study through the reduction or elimination, selectively, of inhibiting factors.

The government could help reduce costs by supporting technology developmentsthat improve design, manufacturing, testing, certification, and maintenance pro-

cesses; including support of related definition, development, and sustenance of data

bases. Other key factors in cost reduction and leadership are new concepts and inno-

vation; pertinent is work related to structural design, manufacturing, certification,

and maintenance processes.

Certification is difficult under normal circumstances, and with composite designs

even more so. The government could review the entire certification process, includ-

ing assessment of technology development needs, and pursue adjustments to the

process that can result in less time-consuming, less costly certification of composite

structures.In all of this work it is important to build confidence in the technology and

processes for handling composites from design to certification. This will require

detailed attention to technology development including large-scale work to validatesmall-scale experimental data and analyses.

Thermosets have received the most attention in past programs. Thermoplastics,

on the other hand, have interesting attributes, such as reproducibility, manufac-

turing simplicity, and high toughness and temperature capability, which may well

outweigh their higher manufacturing costs. These materials should be included in

the program.

Education programs supported by special grants should be developed to t rain

engineers (and technicians) in the application and use of composites.

A summary of key technology program considerations for all aircraft classes th at

should be factored into this planning from a review of government agency consid-

erations is presented in Table S-1-8. The committee did not attempt to identify a

top-level technology development program plan. This level of planning should, of

course, respond to policy and programmatic objectives set by responsible manage-

ment. The committee believes that the government’s program policy, objectives, and

plan should be developed, in concert, within the responsible government agencies

(NASA, DOD, and FAA). This will be a complex undertaking. It is recognized that

the development of an advanced organic composite material technology program is

indeed complex because of the genericaswell as he unique considerations associatedwith aircraft classes and their users.

Regarding materials, the agencies agree that the basic (generic) technology

should be pursued. They believe, and the committee concurs, that the govern-

ment should direct attention to basic R&T and standards for assessing and testing,

and that industry should pursue product development. The value of pursuing mate-

rial technology development includes cost reduction (though not assessed as a major

life-cycle, cost-controlling factor), greater reproducibility, ease of repair, and greater

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T A B L E S-1-8 G o v e r n m e n t A g e n c y S u m m a r y -- T e c h n ol o g y P r o g r a m C o n s i d e r a ti o n s ,Al l Ai r c r a f t C l a s se s

T e c h n o l o e v D e v e lo D m e n t

E f f e c t s o f d i s c o n t in u i t i es ; c u t o u ts , g r a d ie n t s , a n d d a m a g eM o d e l in g a n d f u l l s c al e ; w i n g b o x es a n d f u s e l a g e sh e ll sA i r f r a m e s t r u c t u r a l in t e g r it y , l a n d i n g g e a r s, a n d e l e c tr o m a g n e ti c sAer os t r uc t u r a l t a i l o r i ngF i l a m e n t- w o u n d s t r u c t u r e sM e t ho d s f o r c o n t r o ll in g f a t i g u e a n d s t a n d a r d s f o r d e s ig nSys t em r e sponse t o r epea t ed l oadsSys t em cha r ac t e r i s t i c s ; m echan i c s , dam age t o l e r ance ,

f a i l u r e m o de s, e n v i r o n m e n t a l e f f ec t s, a n d e n e rg y a t t e n u a t i o nS u p p o rt a b il it y ; m a i n t e n a n c e a n d r e p a i r i n d e p o t a n d f i e l dTes t i ng ; bond s t r eng t h , s t an da r ds , t e chn i ques , an d i n s t r um en t sL i gh t n i ng - s t r i ke p r o t ec t i on wi t hou t we i gh t pena l t i e s

Com ponen t s and Sys t em s . Ana l v t i ca l Too l sC o m p l ex l o a d t r a n s fe r s ; f i n i t e e l e m e n t t e c h n i q u e sL o c a l a n d g l o b al s y st e m s i n c l u d i n g f a i l u r e m e c h a n i sm sP o s tb u c k li n g a n d n o n l i n e a r e f f e c t sF a i l u re s a n d d a m a g e g r o w t h

M a t e r i a ls a n d P r o c e ss i n gC h a r a c t e r iz a t i o n ; f l a m m a b i l i t y , t o x ic i ty , a n d s m o k eI m pr oved e r os i on cha r ac t e r i s t i c sT h e r m o s e t re s e a rc h a n d t e ch n o l og y d e v e l o p m e n tT h e r m o p l a s t ic r e s e a r ch a n d t e ch n o l o g y d e v e lo p m e n tM a t e r i a l s a n d m a t e r i a l f o r m s for s eve r e de s i gn cond i t i onsM a n u f a c t u r i n g t e c hn o l o g y; r e p r o d u c i b il i ty , a u t o m a t i o n , a n d

e f f e c t s o n p r o d u c tsDa t a ba se sNondes t r uc t i ve t e s t i ng

Design ConceDt s and I nnova t i onL o w c os t a n d w e i g h tC r i t e r i a a n d s t a n d a r d s ; f a t i g u e , d a m a ge , a n d d u r a b i l i t yD a m a g e t o l er a n ce a n d d u r a b i l i t yS u r v i v a b i li t y , c r a s h w o r t h in e s s , a n d f a t i g u e l i f eS t r u c t u r a l c on c ep t s; e f f i c i e n c y a n d t a i lo r i n gMa i n t a na bi 1 ty a n d r e p a i r a b i 1i ty

C e r t i f i c a t i o n C a D a b il it vDef i n i t i on o f p r oces se s and p r ocedur e sFu l l s ca l e ve r sus coupon r e sponse and s ca t t e rS t a t i s t i c a l ana l ys i s t o r educe t e s t i ng and cos t sS t a n d a r d i z e d p ro c es se s a n d d e f i n i t i o n s

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toughness (reduced damage susceptibility and failure response). Inhibiting factors

today are high material and processing costs, low levels of toughness, high degrees of

response-to-damage, rate-of-failure progression, and the inability to operate at high

temperatures.

SUMMARY OF HEY OBSERVATIONS

In summary the committee notes the following about the development and ap-

plication of advanced organic composites:

Advantages-The potentials for weight reduction, increased performance,

and/or mission flexibility, ease of manufacturing and assembly, and reduced life-cycle cost.

Drivers-Increased performance, mission flexibility, new capability, and for-

eign competition.

Drawbacks-If technology development is not pursued, there are high costs,susceptibility to damage, and limited serviceability and supportability.

Problems-Damage tolerance: design capability (analysis, da ta bases) related

to failure mechanisms, bonds, joints, and other elements; repair; nondestructive eval-

uation; environmenta1 effects; high-temperature capability; low-cost manufacturing;

and certification.

Unresolvable issues-No real unresolvable issues, bu t need management cul-

tural changes, more experience, and facilities.

Government role-Technology development, new concepts (innovat on) for

design and manufacturing, test and evaluation processes, standards, data-bank de-

velopment and support, education, and improved certification processes to build

confidence in design and application. With regard to materials the committee be-

lieves that the government should help develop materials system characteristics,

standards, processes, and techniques for measurement and evaluation of materials,

and leave focus on materials and material system development to the materials

industry.

The committee’s key observations are the following:

0 Despite successful application of organic composites to aircraft, their full

potential is largely unused.

Foreign competition (with government support) has been more aggressive in

applying advanced technology and will continue to be aggressive.

The driver for composites has been performance. The new emphasis must be

on reduced costs-initial, operations, and support. Affordable aircraft is a must for

both civil and military systems.

Innovation and data-base development and documentation are other points

for program emphasis.

New programs must be directed at significant increases in technology: new

ways to design, test, build, and maintain low-cost, high-strain, integrated-structure

0

0

0

0

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aircraft. Selective generic component and system test work is required. Funding for

such work falls short in all government programs.

The military does provide substantive support to R&T programs for highly

Future use of composites depends upon the level of confidence that designers,

project managers, and corporate management have in the available technology.A bold new program will have to be defined and brought to the attention

of NASA and other involved government agency managements, the administration,

and the Congress. P ar t of this program development task will be to make clear the

inseparable roles of government and industry.

Program planning needs to involve the government agencies, industry, and

the universities. The definition, support, and conduct of critical, large, expensive

test programs should also involve these groups, in the form of joint ventures.

Thus, the committee takes the position that the full potential of composites for

aircraft are far from realized, and,

(1) the government’s program must be directed to the future and be appropri-

ately visionary;

(2) it is incumbent on the government (NASA, DOD, and FAA) to provide

the nation, through industry, with the capacity to capitalize on composite material

potential; and

loaded, high-performance aircraft, but this does not relieve the needs noted.

0

(3) a bold new technology development program is needed.

It is the view of the committee that these actionswill provide the nation with the

technology that will allow the design, development, and certification of cost-effective

composite aircraft with high levels of confidence.

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Section I1

Response to Government Issues

and Questions

The role of government in aeronautical technology development, particularly

that of the National Aeronautics and Space Administration (NASA), has beenbrought into question due to budget constraints. This has had an adverse im-

pact on NASA’s support for advanced composite structures work, especially re-

lated to civil aviation. For example, NASA’s fiscal year (FY) 1986 budget for

research and technology (R&T) development was under $4 million. The Federal

Aviation Administration’s (FAA) budget was also quite low, less than $1 million for

safety/certification-related composite structures R&T.Because of its constrained budget for advanced organic composite structures,

NASA raised a series of questions related to a future NASA R&T program: (1) Cana new program help resolve industry needs? (2) Is a long-term major national effort

appropriate? If appropriate, (3) What is the government’s role? (4 ) Where can

the government best apply resources? ( 5 ) What specific program guidance and

priorities are appropriate? and (6) What are the key barriers to the consideration of

composites as routine structural material?

FUTURE R&T PROGRAM

New Program

The committee believes that the current R&T program in government is notdeep enough or broad enough to provide the data required for sound design and

development of advanced organic composite aircraft with reasonable industrial risk.

A new R&T program is indicated if, as a matter of national policy, the United States

wants to maintain a leadership role and a competitive advantage over other nations

in aircraft design, manufacturing, and sales.

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Maor National Effort

The committee believes that a major national effort is warranted in view of

the complexity, high risk, large investment, and high-potential national payoff of

an effective, successful R&T program. A mitigating factor in favor of a national,

appropriate program and appropriately disseminating the program data.

not a private, effort is the little likelihood of industry mounting and sustaining an

Government’s Role

In the view of the committee, the government’s role is to orchestrate the defini-

tion and implementation of an appropriate R&T program with inputs from industry

and the universities. It is anticipated that significant elements of the program will

be carried out in-house and under contract and that some parts of the program

will be joint government, industry, and university activity. This joint activity would

be characterized by large, significant effort having a large payoff in next-generation

designs.

Application of Government Resources

The application of government resources and the identification of program pri-

orities were not addressed by the committee. The committee believes tha t program

funding and priority judgments need to be made in the context of specific future

development program possibilities and agency budgets and priorities, and these

judgments can best be made by the agencies themselves with industrial guidance

and university participation.

Hey Barriers

Barriers to the application of advanced organic composites have been discussed

in detail in Section I of this Supplement. In simple summary, the lack of data bases

and experience combine to affect adversely the time, cost, and certainty of design,

development, and certification of advanced organic composite aircraft and form the

key barriers to accelerated use of these composites.

PROGRAMMATICMATTERS

costs

Costs are possibly the most significant barrier to more rapid growth of compos-

ites. The representative but rough estimate of costs noted in Table s-11-1are for

transport and fighter class aircraft.

Manufacturing dominates structural costs. The committee believes that suc-

cessful investment in manufacturing-processes R&T could significantly reduce total

system cost.

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T A B L E S-11-1 Representat ive Costs of Composi te Structures forTransport and Fighter Aircraft

Cost SegmentCosts (percent)Transports Fighters

ManufactureMaterialQual i ty assurance

and test

55-5030-3515

70-6510-1520

A t least three manufacturing techniques hold some promise for cost savings over

current techniques. These are filament winding, pultrusion, and three-dimensional

weaving or other weaving/braiding techniques. Some technology development hasbeen directed to these areas. However, the committee believes that greater invest-

ments are required to determine the merits of these and other possible processes and

forms of composite materials to enlarge this important activity.

Structures

A government advanced organic composites program plan should be formulated

to provide a new effort in primary structures directed to design and development

activity during 1990-2010. This should entail development of systems and manufac-turing technologies including innovative structural concepts that exploit advanced

composites, particularly for wings and fuselages. An aggressive goal would be for

new designs to have a 50 percent primary structure weight savings with a 50 percent

savings in cost.

The advanced primary structure design concepts would provide greater stiffness,

strength, damage tolerance, and system life. Products of this work would include

an understanding of design requirements and constraints. The innovative structural

concepts work would include tailoring for best use of materials (i.e., do not follow

the practices for metal structures). A n integral part of the effort would involve

textile technology, including three-dimensional braiding, fiber placement, and curing

processes.

This kind of primary structures work will require analyses and design-verification

testing using component and system subscale models and selectively large-scale, in-

cluding full-scale, models. The work would also require the development of analytical

tools and models and the building of appropriate structural design and manufac-

turing da ta bases. Included should be computer-aided design and manufacturing

compatibility. These technology tools will assist in identifying and resolving critical

structura l issues from design to development to certification and operation.

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Advanced manufacturing technology should use intelligent machines and tool-

ing, i.e., robotics with built-in (artificial) intelligence to increase productivity, con-

sistency, and quality. Industry must develop new kinds of factories. The materials

that would be employed would include thermoplastics and advanced thermosets. To

be most useful to industry, this work must be accompanied by the selective building

of appropriate da ta bases.To exploit innovative, low-cost manufacturing methods there must be parallel

development of analytical tools that predict the structural behavior of components

made by the new methods. These analytical tools can form the basis for future design

and manufacturing procedures. Government laboratories should, through in-house,

contract, and grant activity, help develop these analytical tools; and through coop-

erative efforts with airframe manufacturers, fabricators, and universities, produce

and test representative components to verify analyses.

This effort should focus on the development of cost-effective composite struc-

tures through the definition of efficient structural arrangements that can be rapidly

produced by automated material placement techniques. The government can accel-erate this activity by soliciting and sponsoring research to identify new structural

shapes, elements, and components that are amenable to low-cost manufacture.

In preparation for such work it would be desirable to have system analyses that

provide trade-off assessments of manufacturing cost against vehicle performance.

Technology

FIGURE S-11-1 conceptually presents the structuring of an integrated technology

data base for the design, test, and manufacture of composite aircraft. As noted,

the term “material properties” involves such matters as the mechanical, thermal,

chemical, and electrical properties of the composite materials under consideration.

Needed is the definition of the standard (generic) tes ts that characterize the

basic properties of the materials. This includes the identification of the test type

and methods for the measurement of such factors as ensile and compressive strength,

shear fatigue, fracture, and thermal and chemical responses to environmental and

loading conditions. This is not a simple matter. It is complicated by, among other

things, test conditions and specimen geometry.

To be able to compare types of materials, it will, in all probability, be necessary

to test various composite systems (thermosets, thermoplastics, and bismaleimides

or polyimides) for the same application.

The structural elements noted in Figure S-11-1 include such matters as joints;three-dimensional forms; curved, bolted, and bonded structures; and cutouts, holes,

and notches. Important to the designer is life prediction of elements, components,

and systems involving knowledge of such characteristics as damage susceptibility,

fatigue, compression, combined loads, buckling, and environment response. The life

prediction work must be based on analysis and tests. Related documentation must

he developed in a timely manner and in a form useful to designers at large.

The areas of substructure and fabrication include such elements as frames,

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STRUCTURAL

( FEFFbAT:ES ) -Td LEMENTS\ I I 1 I

Mechanlcal

ThermalChernlcalElectrlcal

Etc.

Jolnts3-0 elements

CurvesBonds

cutouts

Etc.

FABRICATION SUBSTRUCTURES

Frames

Fllament PanelsPultruslon Shells

tDATA BASES

DeslgnManufacture

TestCertlflcatlonLlte Predlctlon

Etc.

FIGURE SII-1 Data-base development concept.

trusses, panels, and shells, and such activities as lay up and filament winding. The

government should help define representative tests and perform tests on representa-tive substructures and fabrication techniques. It should assist in the development of

life-prediction analyses and tests.

These and other data would be used to provide the integrated data bases vital

to sound design, manufacture, test certification, and other matters critical to the

development of effective composite aircraft. The type of data-base documentation

needed has to be developed. Here and for the other par ts of the data-base activity

an issue is: Who will develop, update, and maintain these data bases?

Innovat on

The objective of technology development for innovative design and manufac-

ture of aircraft structures is to build the data base to allow designers to produce

components and secondary and primary structures tha t could cost one-half or less

that of current aircraft structures. All types of aircraft are of concern: for the

military-trainers, patrol, surveillance, interceptor, and remotepiloted aircraft; and

for civil-general aviation, agricultural, and business aircraft, and transports.

Approaches to achieving this objective include pursuit of new concepts and

techniques for material and structural design and fabrication. Materials of future

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interest include: thermoplastics, advanced thermosets, chopped fibers, bioadhesives,

biomaterials, self-skinning foam, and hybrid systems. Design innovations involve:

joints, e.g., Windecker wet tow, resistance welded, bonded; foam-stabilized wings

and frameless, stringerless structures, e.g., sandwich skins (supported by various

cover-to-cover sine wave, corrugated, or honeycomb structures); modular systems,

e.g., multicell wing structures and mission adoptive control surfaces; and design andfabricat on procedures for such advanced concepts.

Total factory automation is the direction for the future. Fabrication meth-

ods R&T should include filament winding and molding techniques-resin transfer,

resin injection, compression (for fuselages), and injection (for wing spars). Inno-

vative materials processing should include nonautoclave cure, hot-forming thermo-

plastics, welded thermoplastics (e.g., resistance welding and fusion welding), and

three-dimensional weaving.

GOVERNMENT PROGRAMS

The committee does not believe that the government’s advanced organic com-

posites material and structure program supports the level of activity needed to

realize the full potential of these materials. Industry has not and is not expected to

support the development and dissemination of the data required to accelerate the

application of advanced organic composites by the industry.

The aircraft of interest are both civil and military of all classes. With the

exception of very-high-performance (supersonic, hypersonic, and transatmospheric)

military aircraft, reductions in structural weight and cost of asmuch as50 percent are

possible with new or improved mission and performance capabilities. The technology

leverage gained will not only provide better, less-expensive aircraft with enhanced or

new capability but also provide industry with a competitive edge in world markets.The committee has noted that a new, bold technology development program

is needed. The new program would focus on reduction of design, development,

production, and support costs. It would support innovative work in the areas of

design, test, and manufacture, and assist in rapid, lower-cost certification of resulting

advanced aircraft systems. It would focus attention on new uses of materials as

well as integrated design and manufacturing to make best use of the properties

of composites and void the conservative practice of designs that duplicate metal

structures. The new program would address the problem of building data bases and

the problems of selective collection, documentation, and dissemination of data to

assist design, test, and certification work.Current programs do not address the spectrum of work envisioned in this bold

new program. Funding has been and is expected to continue to be a problem. Itis suggested that the concept of joint government, agency-teagency, and industry-

to-government (including universities) programs be undertaken, especially for large-

scale experimental work, to help mitigate cost problems.

The institutional means appear to be in place to address the matters of program

definition, approval, implementation, and management including reporting and data

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dissemination. It is the committee’s view that it would be appropriate for NASAto take the initiative in the development of the bold new program with strong

participation from the U.S.Department of Defense and FAA, and with the active

involvement of industry and universities.

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Appendix ASynopsisof Presentations to the Committee

Three separate sets of presentations were made to the committee. The first

set took place at a meeting held on December 17-18, 1985 to review government

application and operational experience and research and development activity with

advanced organic composite materials. The second set, February 10-11, 1986, was aforum for aircraft manufacturers, an airline operator, and material manufacturers to

review their individual experiences, problems, and technology needs. The third set,

March 26, 1986, consisted of presentations by government representatives of their

views of technology development needs and plans.

The synopsis that follows contains the general sense of the individual presenta-

tions in the order they were given to provide an overview of the substantive matters

addressed. The views expressed were those of the individual presenters and do not

necessarily represent those of the presenter’s organization.

COMMITTEE MEETING OF DECEMBER 17-18,1985

Application and Operating Experience

US.Air Force (T. Reinhart)

The Air Force has had 8 to 10 years of operational experience with composites,

with good success; composites are being used on rotor blades and other parts of

helicopters and for secondary structures on other types of aircraft. Plans indicate

tha t some 40 to 60 percent of the structural weight of new aircraft will be composites.

Operational problems include cracking and corrosion of met a1 honeycomb, inci-

dents of maintenance damage, quality control in manufacture, paint removal, and

repair.

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The operational environment appears to have had no adverse effects on compos-

ite material and structural characteristics other than corrosion of associated metal

par ts because of inappropriate composite structure design.

In summary, operational experience is good while maintenance experience is

poor. Needs include improved damage tolerance, large-area inspection capability,

understanding of failure mechanism, reliable joints and attachments , and designsth at can efficiently handle the transfer of large loads.

For transport class aircraft, there is a need for more design data for highly loaded

parts.

US.Navy (D. Mulville)

The Navy has had extensive experience with both fixed- and rotary-wing air-

craft composite applications. The Navy is favorably impressed with its application

of composites including the use of composite load-carrying wing skins and engine

casings (replacing titanium).Problems found are related to operations, maintenance, and repair of battle

damage. Care needs to be taken in design where high temperatures can impinge on

composite structures (e.g., hot duct blowouts).

The AV8-B aircraft primary structure is about 26 percent composites by weight.

The JVX/V-22 structure is expected to be 70 percent composites by weight. An

A-6 composite wing-box program is under development, as are studies of composite

control surfaces.

Field repairs of composite structures are a major concern. A substantial program

is in progress with emphasis on the minimization or elimination of the need for special

repair equipment.

Generally there has been little use of thermoplastics, except for repair.

Problems are related to damage during maintenance, erosion/abrasion, and wear

around holes. Moisture intrusion and its impact on metal components is a long-term

problem. Fuel leakage and lightning strikes are other areas requiring special attention

in design and manufacture.

In summary, experience with composites has been good. Operational support

and repairs is an area requiring and getting attention in the Navy program.

U.S.Army (P. Haselbauer)

The major composites experience has been with rotorcraft rotor blades (AH-15,CH-47D, UH-GOA, and OH-58D) and some secondary airframe components. The

OH-58D production articles will have composite main rotor yokes. This yoke has

been through qualification testing. The service is moving toward greater use of

composites in its future rotorcraft.

The types of problems encountered include: rough skins, skin/core voids, fittolerances, moisture retention, retention of blade-tip weights, and the sealing of fuel

in composite structures. Correction of these design and operating problems requires

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detailed attention to design, manufacturing processes including quality control, and

knowledge of the operating environment.

In summary, the Army has found that composites are viable for its aircraft

structures; trade studies that consider costs, weight, performance, and support

dictate the use of composites; three-dimensional stress analyses are important for

design; and the use of composite structures for the containment of fuel should beavoided.

Application and Flight Experience

National Aeronautics and Space Administration (L.Vosteen)

The National Aeronautics and Space Administration (NASA) supported an ex-

tensive flight-service evaluation program for noncritical advanced organic composite

components on a variety of aircraft (L-1011, -737, CH-54B, 06-L,DC-10, nd

C-130). ome of these aircraft are still in operation. NASA has also supported com-

ponent development and transport aircraft flight service on secondary components

aspart of its Aircraft Energy Efficiency program. An extension of this latter effort in-

cluded medium-sized primary components (horizontal and vehicle stabilizers). Some

of these components are in flight service and others are still t o be certified.

In its composite technology program, NASA has addressed environmental ex-

posure, durability and damage, fuel containment, critical joint technology, design

for minimum stress, and impact and damage tolerance. The program also included

the effects of service time on the strength and other characteristics of composite

components.

Ground testing supported the flight program. Unexpected failures did occur in

the ground test work. The failures were associated with fastener fits, interlaminarstress, and stress concentration. In general, it was found that secondary stress

(not important in metal structures) is important in composites. One concern is

that secondary stress may not, and often does not, show up in specimen and smallcomponent tests where full-scale loadings and constraints are not and cannot be

simulated.

Studies of manufacturing costs show that composites, in quantity, may be less

costly than metal structures. They have fewer parts and fasteners and often require

less labor, but production automation will be a key factor in gaining competitive

costs.

The NASA research and technology (R&T) program includes work on damagetolerance, lightning protection, heavily loaded wing joints, and design concepts for

increased stress tolerance and reduced acoustic response.

In summary, in-flight component durability, weight savings, and design and

analysis methodology have been successfully demonstrated, and damage tolerant

concepts for panels (of wings and fuselages) have been defined. Major needs are seen

to be reductions in manufacturing costs, improved damage tolerance, low-cost re-

pair techniques, designs that minimize out-of-plane loads and stress concentrations,

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understanding of acoustic transmission and fatigue, understanding of the impact dy-

namics of structures, and full-scale verification of large system (wing and fuselage)

design technology.

Certification and Operational Experience

Federal Aviation Administration (J. Soderquist)

A number of carbon-epoxy structural applications are currently being evaluated

by the Federal Aviation Administration (FAA) and a number have been approved

for use on transport, general aviation, and rotary-wing aircraft that have been man-

ufactured both in the United States and in Europe. Included in the applications

currently undergoing FAA type certification are several all-composite general avia-

tion aircraft.

The earliest carbon-epoxy applications certificated were the B-737 (1973) spoil-

ers and an engine nose cowl outer barrel on the DC-9 (1976).

A structural certification program typically includes material property develop-

ment, static st rength and damage tolerance substantiation, impact dynamic evalua-

tions, and lightning strike evaluations.

A number of issues have been identified that require further research and de-

velopment (R&D) effort. One example is that of mechanical property test methods

in the material property development portion of a certification program. There

are currently more than 10 in-plane shear test methods utilized to one extent or

another-all yielding different results.

Work is also needed in the following areas: statistical procedures to reduce the

amount of material property testing of environmentally conditioned specimens, ananalysis methodology capable of predicting material and st ruc tural response due to

environmental considerations for use in ultimate load static strength assessments,

failure criterion, and design criteria for s truc tura l fasteners.

The st ructural integrity of bonded structure is an area of concern. A number

of struc tural bonds have failed in-service and during certification testing. There are

no nondestructive inspection techniques available to detect understrength bonds.

The degree and level of testing adversely impact costs. A composite material failure

analysis capability must be developed.

Current FAA R&D activities include: sensitivity of fuselage structure to frag-

ment impact, repeated-load evaluation methodology, an engineering textbook, and

an inspector’s handbook. Work is proposed that would (1)develop a nondestructive

inspection technique capable of screening out understrength bonds, and (2) develop

a failure analysis capability.

In general the operational experience with composites in civil aircraft has been

excellent. This is attributed, in par t, to the use of 350°F cure material systems,

reduced design strain levels, and bolted structures.

A standing list of R&D topics include:

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Effects of load truncation and load sequencing on the repeated-load response

Pressurized fuselage damage containment concepts;

Statistical variability associated with the initiation of detectable damage and

Nondestructive test methods capable of detecting understrength bonds;A primary adhesively bonded structure (PABST) program aimed at develop-

ing the technology to design and fabricate repeatable and reliable metal-to-composite

and composite- ec om posi e bonds;Material systems having: laminate Grc= 5 in-lb/in2, fiber stra in of 2 percent,

and laminate transverse strain of 0.6 percent;

Determination of fuselage and seat structure response to crash loads;

Flammability/toxicity/smokecharacteristics of composites;

0 Failure analysis methodology; and

0 Mechanical property test methods.

of aircraft structures;

damage growth;

Research and Technology Programs

National Aeronautics and Space Administration (S . Venneri)

The NASA organic filamentary composite program is being reassessed; it is in the

planning stage and open t o (committee) comment. The objectives for thermosets

and thermoplastics are: developing new material concepts and understanding of

behavior, including failure mechanics; enabling innovative structural designs and

applications; and assisting the achievement of “full” weight and cost savings, and

performance gains in future aircraft. The s tructural weight savings are estimated to

be in the range of 25 to 35 percent.The technology cannot be developed without work on complex structures. How-

ever, NASA’s large structures (systems technology) programs have been dropped

because of budget constraints. These programs were related to large transport wing

(C-130 wing box and high aspect ratio [12] ual spar wing) and fuselage technology.

In the latter case, some small-size panel work continues.

The budget cut in fiscal year (FY) 1985 or systems R&T was $25 million. The

R&T base program remained in the $4 million to $5 million range. These budgets

cover contracted R&T, not in-house staff and support. The plan is to add more

funds in FY 1986 to the R&T base program. However, the budget level is such that

largescale R&T work will not be supportable.Some detailed wing R&T is planned relating to durability and damage, fuel

containment, lightning damage avoidance, and critical joints. Fuselage work planned

includes: damage tolerance, pressure containment after buckling, cutout and joint

design, impact dynamics, and acoustic transmission and characteristics.

The NASA program is to be a combination of in-house and industry activity

th at will include material concepts, structural concepts, and fabrication techniques.

Industry will be most active in this latter area. Related technology work to be

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pursued will cover aerodynamics, acoustics, active controls, and interdisciplinary

design and systems integration. The planned program on structural concepts will

focus on tailoring for concentrated loads and aeroelastic behavior.

The new materials work will address tough matrix resins, new material forms,

and fabrication technology where costs me an important factor that must be ad-

dressed with industry participation. The concept verification work planned, thoughanticipated to be very limited, will involve definition of concepts in some detail,

research models, and large element panel/attachment combinations. The modeling

work is to include three-dimensional analyses.

In gross the plans for the advanced organic composite program (FY 1986 to

FY 1990) are expected to contribute, in some degree, to verified, cost-effective ad-

vanced composite, primary structural concepts for wings and fuselages, and address

material forms, high-performance polymers, characterization of advanced systems,

composites-processing science, and structural element and structural component

fabrication.

The NASA program will also encompass metal matrix composites for airframeand propulsion systems through the use of a small business, innovative research

proposal activity. This will not be a large effort since the U.S. Department of

Defense (DOD) has a significant metal matrix composite program under way. The

major thrust of this program will be directed to fundamentals as they relate to fiber-

reinforced superalloys for propulsion systems, light alloys for aeronautic (and space)

structures, and selected hardware-oriented efforts (mostly for space structures).

NASA is planning a significant move into thermoplastics. The program will hold

proper balance between thermosets and thermoplastics. In summary, the future

direction of the NASA program will emphasize: the development of anisotropic ad-

vantages of composites for advanced structural designs (30-40 percent); fundamental

understanding of materials (30 ercent); innovative use of new materials (including

low cost); and structural analysis and design technology.

U.S.Air Force (D. Roselius)

The U.S.Air Force composites technology program for the 250°F range has

been essentially completed. Work on composites useful in the 27SoF-450"Frange is

moving from the DOD 6.2 (R&D) category to the 6.3 (applied) category. Work on

45OoF-70O0Fcomposite systems is starting with emphasis in the 6.2 category and

some work in 6.3.

This R&D program gives credence to the projection that future Air Force air-craft, by weight, will be composed of 50 to 60 percent composites.

The major concerns in the composites arena relate to the understanding of

damage and failure mechanics. Composites do not behave like metals. New design

approaches are required for composites. Thus, there is a need to develop unique

specifications for composites (similar to 83444 for metals). Requirement documents

on durability, certification methodology, and damage tolerance are being drafted.

The Air Force has and is supporting large-scale (wing, fuselage, and component)

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composite systems R&T development. Manufacturing technology is included in this

activity.

Some key design issues requiring technology development are: bolted-joint anal-

yses for strength and life, high stress and strain design, analyses and test techniques,

design optimization, ballistic and laser impact, and survivability and supportability

damage tolerance and maintenance.High priority is attached to bismaleimides for high-temperature applications.

Some of the major issues are reproducibility and toughness.

Special attention is being given to thermoplastics because of projected advan-

tages such as low manufacturing costs (no cold storage or autoclave cure required,

possible to automate, and postforming capability) and good engineering properties

(resists impact damage, high elongation/increased allowables, low moisture absorp-

tion, damage is visible, slow crack growth, and potential for reduced fire/smoke

hazard).

For thermoplastics, the Air Force is examining manufacturing procedures for

reduced costs and improved performance, improved damage tolerance, increased

design flexibility, and ease of supportability.

The Air Force also has an effort on the use of organic composites for low ob-

servability. This entails demonstrations of full-scale components and in-line service

practicality.

Carbon-carbon materials are receiving special attention because of their long-

life, high-temperature potential for propulsion system applications.

Ordered polymers are of special interest because of their potential for providing

high-specific strength in combination with high-specific modulus.

In summary, the Air Force has a continuing interest in composite materials

for aircraft systems with emphasis on material improvement, higher-temperature

capability, supportability, durability, damage tolerance, and design and manufac-turing technology development. Program plans have been defined through FY 1990

covering graphite-epoxy structures, ballistic survivability, laser survivability, and

structures beyond graphite-epoxy.

U.S.Navy (D . Mulville)

The Navy’s program stresses high-strain wings, low observability, advanced land-

ing gears, and supportability for designs to fly in the 1990 to 2000 time frame. The

program has two major elements: structural mechanics and aircraft structures tech-

nology. The division of effort is approximately 20 percent and 80 percent, respec-

tively.

The structural mechanics activity includes impact damage mechanisms, mod-

eling for fatigue and fracture analyses, and damage tolerant structures. Structural

dynamics work includes aeroelastic tailoring.

The aircraft technology effort includes advanced design concepts, structural

durability and certification, supportability (repair and damage acceptance criteria) ,

loads and system life management, and electromagnetic compatibility and effects.

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U.S.Army (P. Haselbauer)

The Army program is directed to rotorcraft and encompasses basic research,

exploratory development, and advanced development covering manufacturing and

processing methods and systems.

The basic research effort includes work on toughened resins and high-strain fibersfor energy absorption. Projected work includes postbuckling of thin-gauge materials,

coupling (structural) of composite rotors, failure criterion, and energy absorption.

The exploratory and advanced development work is directed at rotor systems

(blades, hubs, and controls) and the airframe (lightly loaded structures, primary

structures, and landing gears).

Work is in progress to develop damage tolerance and durability criteria for

composite structures, improve fatigue analytical techniques and methodology, and

develop vibration reduction techniques and analytical procedures. The results of

these efforts coupled with structural component test and flight data recorder efforts

will culminate in a helicopter structural integrity program for both metallic and

composite structures.

The advanced development program resulted in the following accomplishments:

blades with less drag (5 0 percent), fewer parts (50 percent), less cost (15 percent),and less weight (20 percent); a multitubular spar system; and bearingless main rotor

and fiberglass rotor blade concepts. As a result of these earlier efforts, composite

rotor blades are the accepted norm for helicopters. There are composite rotor blades

on the CH-47D, CH-46, and AH-18, and they are soon to be introduced on the UH-

1H. Product improvement programs will most likely provide composite rotor blades

for the UH-60 and AH-64. Additional effort is planned t o develop techniques and

procedures for quantum improvement in producibility and cost reduction.

A full-scale flex-beam composite hub is under development for the AH-64helicopter, and a whirl tower test is scheduled for mid-1987. A flight test is planned

for early 1988. The flex-beam concept will reduce cost, weight, and drag while

improving reliability and maintainability.

An advanced technology retractable landing gear is under development to reduce

drag and provide improved crashworthiness capability. Full-scale drop tests are

scheduled for mid-1987.

Initial efforts on composite tailbooms and stabilizers led to the demonstration

Advanced Composite Airframe Program (ACAP). The ACAP had as its major ob-

jectives the demonstration of damage tolerance, crashworthiness, and repairability.

In addition, it had the objectives of demonstrating the benefits of cost and weightsavings achievable with composites, the establishment of a credible cost data base,

and the reduction of risks in committing to the development of composite primary

structures.

The Army program was funded at about $25 million in FY 1986 (excluding

manufacturing work).

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Committee on Net Shape Technology (M. Steinberg)

Dr. Morris Steinberg, chairman of the Committee on Net Shape Technology

the committee’s activities, noting in particular the work of Workshop 111, Future

The workshop was focused on the net-shape manufacturing of composite struc-

tures as part of the AFSB’s examination of net-shape manufacturing. The program

covered Air Force Program Overview, Factory of the Future, Technology Issues

(thermosets, thermoplastics), Metal Matrix, Carbon-Carbon/Ceramic Matrix, Raw

Material, Material Forms, Tooling and Processing, Quality Control/Repair, and

Carbon-Carbon for Hot Airframe Parts and Engines.

The purpose of the meeting was to identify government and industry technical

and financial needs to accelerate the development and transfer of technology and i ts

application for low-cost composite manufacturing. The questions to be addressed

were: What are the drivers? What technical and institutional bottlenecks exist?

How are processes and products th at are reproducible and affordable to be achieved?and What should be done to accomplish this?

The field of composites evolved from the 1960swith emphasis on performance

priority t o the 1970s with emphasis on manufacturing methods to the 1980swith

emphasis on quality control, costs, maintainability, and repairability.

Technology needs were identified as relating to: many small and medium-sized

manufacturing technology programs; more technology transfer workshops to identify

key technology issues and approaches to their resolution; establishment of specifica-

tions for product ion-ready prepregs; guidelines for assessing and repairing manufac-

turing defects; selective funding of automation projects; and material specifications

and characteristic requirements for thermoplastics.

Manufacturing needs were identified as relating to: microprocessor controls

for in-process quality control; greater interface and interaction between materials

processors and manufacturers; more literature on processing science, technology, and

practice; and improved data bases on materials, processing, and computer modeling.

Regarding thermosets, there are concerns over relative brittleness and the slow,

costly processing of parts. The quality of prepreg hampers automation and causes

problems relating to reproducibility, defects, and reduced tolerance to physical and

chemical environments. Poor prepreg properties also adversely impact labor costs,

rejection rates, and rework. The adverse impacts carry over to end products in the

form of reduced durability and reliability, reduced design strain (some 40 percent)

resulting in overdesign, and loss of potential performance and increased cost.Regarding resin-matrix thermoplastics, they can provide greater toughness and

are less expensive to fabricate while providing high-strain potential and better dam-

age resistance and tolerance. However, these materials are relatively new t o aircraft

and, thus, limited experience and data base exist. Creep and fatigue characteristics,

especially at high temperatures, are not fully known.

The workshop resulted in the identification of the general needs as follows:

of the National Research Council’s Air Force Studies Board (AFSB), summarized

Composite Manufacturing Technology.

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integration of design and manufacturing;

better data-base and design guides;

automation with specific attention to reduced costs, improved consistency,

and reduced labor content;

sensors that control processes, material production, and quality, and reduce

reject ions;improved nondestructive-testing techniques;

improved curing concepts;

tooling development; and

improved repair techniques.

The workshop is to produce road maps for a program (including program costs)

th at will increase composite net-shape productivity and cost-effectiveness.

INDUSTRY FORUM OF FEBRUARY P0-11,1986

Large Transports

Boeing Aircraft Company (J . Quinlivan)

Composites have been and are applied in many nonprimary, important parts on

current transport aircraft. A t Boeing, some 300,000 pounds of composites per year

are used in production aircraft. Damage tolerance is a critical concern and requires

extensive testing.

Boeing is examining the use of composites for primary s tructural components

(wings, stabilizers, and aft fuselage body) as well as for secondary structures. The

new JVX (tilt-rotor) aircraft will be essentially an all-composites aircraft.

Inhibiting factors relate to costs of manufacture as well as the production facil-ities themselves. However, progress is being made on cost reduction. At present, in

spite of greater costs for materials and tooling for a composite wing, it is estimated

th at a final cost would equal tha t of an aluminum wing. Other inhibiting factors

are: material limitations, design and certification uncertainties, and the levels and

amount of testing required.

Compared to present conventional composite design, the proper application of

advanced composites can reduce costs by some 20 to 30 percent through reduced

parts, weight, and production and increased strength.

Further cost reductions should be possible through innovative design, the use of

computer-aided design and manufacturing (CAD/CAM), and automated produc-tion. In the future, thermoplastics should have a role. The outlook is for composites

to become some 60 percent of the total airframe by weight by the late 1990s.

Although new organic-matrix composite materials show much promise, they are

not well understood from behavior and performance considerations. An important

consideration is the ability to verify analyses by testing.

New organic-matrix composite technology developments need to focus on fuse-

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lages, empennage, and wing applications addressing matters important to operations

such as damage tolerance, repair, durability, flammability, fire and lightning protec-

tion, and electromagnetic effects. Other important matters related to design and

production include joints, cutouts, impact dynamics, acoustics, and postbuckling

integrity.

Certification is a significant issue. The Boeing philosophy is “certify by analysessupported by test evidence.” There is a need to advance analytical techniques

to handle the technical matters noted and to reduce test and certification time

and costs. The analytical tools must handle both macro- and micro-engineering

assessments. Just as important is the development of simple, consistent, standard

test methodology that can assist in proof-of-design analysis and cover such matters

as load distributions, large deflections, accelerated testing, failure processes, effects

of environment spectra, and residual strength after failure.

Technology development is needed for integrated thick and thin structures tha t

cover understanding of materials and, more importantly, effects of processing, de-

sign methodology, damage tolerance assessment, prediction of and assessment of

allowables, and response to service environments.

McDonnell Douglas Corporation (H . C. Schjelderup)

The introduction of composite materials in commercial aircraft structures has

been slow compared to their introduction in military aircraft. Flight service compo-

nents, such as the Boeing 737 spoilers and the Douglas DC-10 aft rudder, have been

in commercial airline service for over 10years without any serious material problems.

As a result of these and other flight service programs and NASA-sponsored research,

composites are in production for the Boeing 757 and 767, the McDonnell Douglas

MD-80, and the Airbus 310.

Most composite design and manufacturing engineers support the position thatthe state of technology allows production commitments to all structural components

except wings and fuselages. For these two primary structural components, differ-

ences in opinion center around damage tolerance and manufacturing cost; not that

a wing or fuselage could not be designed, but will they be structurally efficient and

economically justified. Recently NASA terminated fuselage and wing technology

development programs that could have helped resolve design questions about such

structures.

Douglas uses classical numerical and semiempirical methods of analyses appro-

priate to the class of structural system problems being addressed: predominantly

simple and elastic in nature; large and complex; large displacements; many variables;and/or strength and fracture dominated.

Design and analyses are supported by material characterization programs for

every new material used in production. Representative data developed include qual-

ification and allowables for strength and elastic properties, environmental effects,

fracture properties, and bonded- and bolted-joint properties. All composite sub-

assemblies are inspected for voids, porosity, inclusions, and delamination by avail-

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able techniques. New techniques for nondestructive testing are under study, i.e.,

backscattering, leaky Lamb waves, and computer analyses.

Emphasis is being put on raising design strain levels while holding stiffness to

make composites more competitive for primary structures.

Current Douglas composite designs operate a t low-stress levels to increase dam-

age tolerance. To date, testing (coupon and subsystem) does not indicate a limitto the life of operational structures. Accelerated testing is limited. It cannot be

used where friction overheats components or where certain types of failure modes

could be missed, i.e., creep-rupture. Compressed real-time testing is used in such

structures.

Experience shows that the following technology development should be pur-

sued for heavily loaded structures: compression failure-associated with laminated

structures with out-of-plane (transverse) loads; tension failure-associated with

strength but more importantly with edge (delamination) failure; interlaminar fail-

ure-associated with thick, heavily loaded structures and, in particular, with out-

of-plane stresses;yoint analysis-addressing load distribution among bolts, inducedtransverse tension associated with combined loading, combinations of orthogonal

and bolt loads, and automated handling of finite analyses of bolt combined with

in-plane loads; hydrothermal stress-associated with heat and moisture in the pro-

duction process, a problem for thick laminates; damage tolerance-for large complex

structures considering the application of finite element analysis through development

of orthotropic, elastic-plastic, crack-tip, and delamination elements (the mechanisms

of crack or delamination propagation) and analytical techniques for applying the re-

sults of coupon and panel tests to full-scale components.

Because testing is time consuming and expensive, effort is warranted on devel-

oping semiempirical approaches to analyses to reduce the need for extensive testing.

Wider, more extensive use of composites is inhibited by a lack of applied expe-

rience. This causes unknown performance, schedule, and cost risks. It is believed

that the technical risks are reasonably known and solvable but producibility and

production costs and scheduling are not. Costs are a significant commercial de-

velopment deterrent. However, there are positive drivers for composites: reduced

weight, corrosion, and fatigue; lower costs (potentially); and the ability t o tailor the

structure elastically. Tailoring, the ability to change structural characteristics in all

directions, is a major and beneficial difference between composites and metals.

Damage tolerance in primary structures for commercial aircraft is a major con-

cern requiring an ability to assess fully any nonvisible damage. currently, Douglas

uses the “MIL-Prime” damage tolerance criteria for composite primary structures(under development by the Air Force). The FAA has yet to develop damage tol-

erance criteria for composite structures, such as wings. The establishment of such

criteria will require evaluations of damage sources, inspection intervals, and damage

tolerance properties.

Thermosets and thermoplastics both have future roles. At present, the use

of thermoplastic is inhibited by high costs and the need t o develop technology

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related to such matters as joining, repair, creep, solvent sensitivity, and automated

manufacturing.

The technical barriers to wider use of composites include:

Damage tolerance (and its predictability). Additional research is warranted

related to safety of flight-a first-order issue.

Electromagnetic effects. Due to the low electrical conductivity of composites,

the designer has special problems-lightning protection, electromagnetic interfer-

ence, antenna design and performance, and electrical hazards for personnel.

Material da ta base. This is a difficult issue because of the “no limit” of ma-

terials, their combination, and their processing. An industry standard for materials

property testing is required for the development of handbook data. Related prob-

lems involve keeping the standards current and the introduction and acceptance of

new materials.

Analytical tools. These are generally good but not always adequately appli-

cable to through-the-thickness forces without very complex finite element modeling.

A valuable addition would be three-dimensional, laminated-element techniques tocharacterize such forces.

0 Adhesive bonding integrity. Bonding is very process and preparation sensi-

tive. There is a need for ways to simplify and assure process integrity and quality.

The technology development needs that are most critical to commercial trans-

por t development relate to program cost. It is believed that technical and engineering

issues can be resolved in development programs. A valuable contribution would be

the generation of design, production, and process cost models for representative

designs.

As to the question of NASA support of FAA certification activity, it is not rec-

ommended that NASA be directly involved unless asked for expert advice. However,NASA is encouraged to increase its large-structure feasibility work and to continue

its R&D programs with industry and university involvement. Timely government

involvement and support for basic R&D oriented activity is particularly important

from competitive and military considerations. Effective data dissemination is also an

important government role and would serve to minimize duplicative and expensive

work within industry. The government should also support high potential payoff

work tha t is beyond the ability of individual corporate R&T programs to support.

Lockheed Corporation (R. L. Circle)

For technologies in transition there are three kinds of forces that can acceleratetheir application: improved performance, reduced costs, and the political environ-

ment. Composites present a real challenge since they require major changes in the

design, development, test, manufacture, and operation processes.

The application of composites in fighters is driven by the potential for per-

formance improvement. The same is true to some degree for bombers. The driver

for transport aircraft is cost, initial and life-cycle-that is, lower costs with particular

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attention to low development risk. Today, there are fighters with composites making

up 30 (and going to 60) percent of the airframe weight, including primary structures.

For transports, the number is some3 percent with continued application to secondary

structures and the potential for some application to primary structures.

The technology issues associated with scale-up and materials from fighters to

large aircraft (bombers and transports) are significant. Differences concern struc-tural design and the amount of material to be processed, some 1,300 pounds versus

100,000 pounds of composites, respectively.

It is clear that the Europeans are making significant commitments to using

composites in transport aircraft. The most aggressive application has been in the

70-passenger ATR-72 center wing box.

The introduction of composite primary structures to transports will depend on

a clear understanding and response to what the industry sees as the issues related

to a full commitment. There must be confidence that the payoffs warrant the risk.

This requires an adequate technical data base, the ability to project costs accurately,

and reasonable assurance that contracted schedule, cost performance commitmentscan be met. Therefore, technology development programs that demonstrate and

validate the technology and performance are required to allow sound cost trade-off

assessments.

Lockheed’s operating experience with composites (C-141 ing, leading edges,

and petal doors) has been good. The costs for manufacturing these parts are below

those of metal par ts, even though the composite parts were essentially hand lay-ups.

As part of NASA’s Aircraft Energy Efficiency program, Lockheed designed a com-

posite L-1011 vertical fin. Based on this experience, the importance of tying design

and manufacturing closely together was clearly demonstrated. It was projected that

through parts reduction and automation the cost of the composite fin would be

$133,700, compared to $195,500 for a metal fin.

The NASA program approach to assist industry (i.e., soliciting ideas from indus-

try, funding studies to define critical technology, coordinating industry technology

development and validation, and emphasizing technology transfer) is strongly en-

dorsed and should be continued.

The NASA/Lockheed composite wing program for large aircraft has been re-

structured because of funding reductions in the NASA systems technology program.

The new program eliminates all validation work and concentrates on design opti-

mization, innovation, new materials, and fabrication methods for such wing elements

as covers, spars, stiffeners, planks, and fuel containers.

This restructured program will not provide the level of confidence desired for afull commitment to the application of composites to large primary wing structures.

There are other programs tha t will help build confidence: Air Force Materials

Laboratory (AFML) large fuselage and manufacturing technology (MANTECH),

V-22, and the advanced technology bomber. However, these programs collectively

fall short of providing and validating the technology data base for large transport

aircraft. Another problem is that there is no dedicated effort directed at industry-

wide technology transfer from these limited programs.

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New programs are needed that:

Give adequate attention to innovation and apply the unique characteristics

0 Do not duplicate metal designs;

Direct at tention to the integration of manufacturing into design;

Include full-scale design and performance validation; andAssure industry-wide technology transfer.

The new program should: address transport wings and be jointly supported

(NASA/AFML); include full-scale validation work (NASA-design, materials, and

analysis; AFML-tooling, manufacturing, costs); emphasize low-cost, low-risk, oper-

ational supportability and design-manufacturing innovation; and develop new anal-

ysis and test technology.

of composites;

Rotorcraft

Bell Helicopter Textron (K. Stevenson)

The use of composites in rotorcraft development has been more aggressive than

in conventional aircraft. Today, designs incorporate some 8 percent metal. The use

of composites is almost complete, having been applied to rotor blades and hubs,

fins, landing gears, pylon supports, fuselages, and, in the case of the V-22 ti lt rotor,

the wing. This has been driven by military requirements for higher performance

and increased operability, both dictating lower weight and improved supportability.

These requirements demand stiffness, tailoring of natural frequencies, crashworthi-

ness, lightweight materials, and damage and ballistic tolerance. These demands are

met by composites.

The application of composites to rotorcraft has proven very effective. One signif-

icant advantage is the ability to tailor stiffness, load path, and failure modes. Com-

posites also reduce corrosion, weight, cost, and fatigue failure. Filament winding,

honeycomb-core tape wraps, and bonding have been used with success. Materials

include fiberglass-epoxy and carbon-epoxy tape (T300/788).

Future technology development should concentrate on easily utilized analytical

techniques for design, material specification standardization (companies use different

specifications), development of consistent approaches to specifying allowables, and

standards for nondestructive inspection (a big problem).

Boeing-Vertol (C. Albrecht)

Rotorcraft are weight, fatigue, vibration, and control critical and have much less

constancy of structure than conventional aircraft. Many of the response character-

istics of a rotorcraft are not known, definable, or understood until flight because

of rotor-imposed loads. With the maturing of the industry, design philosophy is

changing. Earlier designs emphasized safe-life, with some 58 percent of the dy-

namic component weight dedicated to safety. Present design philosophy emphasizes

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T AB L E A-1 P e r f o r m a n c e C o m p a r i s o n s o f M e t a la n d C o m p o s it e R o t o r B l ad e s

Navy A r m yM eta l Co mp o s i t e Co mp o s i t e

Me a n - i m eb e f o r eu n s c h e d u l e dr e m o v a l ( h o u r s ) 135 2,050 1,500

damage and defect tolerance, with dynamic component weights of some 80 to 85

percent dedicated to multiple load-path capability and some 10 to 15 percent single

load-path capability.

Work on composite rotor blades started in 1957. The decision to use compositeblades for production systems was made in 1970. Through late 1985, Boeing-Vertol

had no failures of these blades, compared with 17 metal-blade failures over the period1962 o 1973.Performance of metal and composite blades can be assessed in Table

A-1 from Navy and Army data on mean-time (hours) before unscheduled removal.

Cost has favored composite blades over metal blades by a factor of about 1 to 2 on

the basis of manufacturing man-hours per pound.

A decision was made in 1981 to use composites for all possible elements of the

dynamic system on Boeing-Vertol’s twin-rotor Army 360 aircraft. This involved

blades, hubs, rotor shafts, transmission covers, and pitch housing. The resulting

weight savings was 1,394 pounds (17 percent) over the metal system. All of thesecomposite systems are being tested.

In Boeing-Vertol’s experience, composites have shown the following failure char-

acteristics: fiberglass-soft, slow, detectable with a low sensitivity to notch fatigue;

graphite-unaccept able modes for critical components; and hybrids of fiberglass and

graphite (50-50 pe rcen t) -sof t with stiffness and tailoring flexibility. Composite-

blade root ends have been shown to have high damage tolerance in tests with dam-

ages imposed after 4 x IO6 cycles at design loads. Other parts have shown high

tolerance to damage and fail-safe capability with careful design.

Composites have also shown good fatigue life in a rotor shaft application with a

design that weighed less than an aluminum shaft and considerably less than a steel

shaft. A composite application to an advanced rotor hub resulted in a st ructure hav-

ing 25 percent less weight, 60 percent fewer parts , and 60 percent fewer maintenance

hours.

The company has set its own general design objectives for composites for flight-

safety-critical rotorcraft components:

0 Fiberglass for damage and defect tolerance.

e Graphite for stiffness to a limit of about 50 percent.

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Fiberglass to sustain limit loads.

0 Basic structures are to take ultimate loads without fiber failure and limit

Basic structure mean 2-sigma fatigue strength should exceed maximum an-

Basic structural life should be in excess of 10,000 hours based on 3-sigma

loads without interlaminar failure.

ticipated steady-state vibratory loads.

allowables with “soft” observable damage tolerant failure modes.

Composites are used for 360 airframe components; fuselage, flooring, fore and

aft transmission, landing gear, and engine supports. The benefits are 25 percent in

weight savings, freedom from corrosion, a 45 percent reduction in recurring costs,

and a 90 percent reduction in tooling costs. The frame, stringer, and panel design

has been substantiated by s tatic tests tha t will be followed by shake tests to validate

NASTRAN analyses. At 5,017 pounds, the weight saved over a metal structure is

estimated to be 1,389 pounds (about 22 percent).

The rotorcraft industry has applied composites with considerable success to high-

cycle, fatigue-loaded primary structures. Composites can provide characteristics

(soft failure, damage tolerance) for safety critical components not possible with

metals. Increased life is realized because of high fatigue to ultimate strength ratios.

Additional research should be conducted with hybrid structures for safety crit-

ical components. This includes improved analytical capability especially for com-

plex, thick-laminated dynamic structures. Generic research should be pursued for

optimization of design and development of design guidelines to account for creep

relaxation in fits and clamps.

An issue is how to test under high-frequency loading. Needed are test and

analyses techniques th at can account for cumulative damage and sequential loading

of safety critical components. More needs to be done to understand the propagationof defects associated with long-term, low-amplitude, high-frequency disturbances for

both fixed and dynamic components.

In addition to complex analytical tools, the industry needs simple, quick design

tools for preliminary design and analyses. The industry also needs design guidelines

for controlling failure modes. A related matter is crashworthy design concepts forprimary structures.

Work is needed to develop a better understanding of environmental effects

(hot/wet) on thick composite structures used in dynamic systems.

To get costs down, close interaction and optimization is needed between engi-

neering design and manufacturing.Much of NASA’s composites research and technology development work has been

directed at systems designed for sta tic strength and low-cycle fatigue. To assist ro-

torcraft, the research and technology development should include three-dimensional

structural analyses, mechanical attachments, joints and lugs, fatigue-life analyses

techniques, high-cycle fatigue effects, simple rapid techniques for preliminary design,

failure mechanism control, crashworthiness concepts, and environmental effects on

thick components.

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McDonnell Douglas Helicopter Company (R. M. Verette)

The company has had a long involvement with composites in rotorcraft. Mc-

Donne11 Douglas Helicopters (formerly Hughes Helicopters) used mostly fiberglass

epoxy for the Model 500 and Kevlar epoxy for the AH64A Apache. Par ts produc-

tion has principally involved 250°F curing materials and a range of conventionalmanufacturing processes.

Research and development programs have included landing gears, crashworthi-

ness, tail and main rotors, pitch cases, flex beams, tail booms, and vertical and

horizontal stabilizers. The program has included element level tests as well as se-

lective flight tests. The company has experience with filament winding and with

graphite as well as Kevlar and fiberglass epoxy systems.

The company is making a major investment in a new plant a t its Mesa, Arizona

facility. Of the 340,000 square feet in the Advanced Development Center, 65,000

square feet will be devoted to composites and will be outfitted with existing and new

equipment.

Recommended future actions include generic work to identify (characterize) the

best materials and processes for particular applications considering such factors as

cost, schedule, and quality of product. Included in this work should be such matters

as automation, processes (including co-curing), computer-aided design and manu-

facturing, CAD/CAM utilization, and product property improvement. Tooling, in

itself, warrants study. Matters such as initial and life-cycle costs, production lot size

influence on tooling materials, adaptability, and life are important considerations.

For technology development, full-scale tests are essentially mandatory, i.e., for

crashworthy prediction, design, and performance correlation.

Nondestructive evaluation techniques still warrant technology work. Techniques

are needed that can be used with all types of composites (Kevlar, carbon, fiber-glass, and new resin systems). An important consideration is using nondestructive

evaluation techniques tha t operate at production line rates in conjunction with the

production line.

Toughened resin systems have a real future. Work should focus on the compat-

ibility of the fibers tha t will be applied. Thermoplastics for secondary structures

should be included in future generic technology development programs. They have

other than strength benefits, i.e., shelf life and cost-effectiveness for appropriate

applications.

Sikorsky (B. Kay)

Composites are being used in current designs (some10 to 20 percent of airframe)

with good results. The new S-76B rotorcraft will make relatively good use of com-

posites. A basic issue is productivity with consistency. Fundamentally, composites

reduce weight, parts, fasteners, and tooling for manufacture. These are forceful

drivers for more extensive use of composites.

Sikorsky is working with an Italian firm on the production of an all-composite

fixed-wing aircraft, the composite structure being the Sikorsky contribution.

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The lack of material dat a bases is of concern. Although analytical techniques are

essentially adequate, more technology development is very desirable especially for

the handling of complex loading cases and complex structural systems. Rotor heads

are an example where improved design and analytical techniques would be very

beneficial as would be better materials for such high-stress components. Sikorsky’s

experimental all-composite rotorcraft flight test program was accelerated (with lim-ited component testing) t o speed up the validation of the design, provide early cost

da ta, and hold program costs down. This is not a universally suggested approach

given the present state of experience with all-composite design.

It is recommended that attention be directed at the use of universities for ex-

panding technical knowledge; training professionals in the field of composites from

design, development, manufacturing, and test considerations; and the standardiza-

tion of analyses, testing, and materials. The latter, it is recognized, will be difficult

because of the broad range and changing nature of materials.

High-Performance Aircraft

Grumman (R. N.Hadcock)

Organic composites development work started at AFML in 1964and was applied

to a Navy F-14 horizontal stabilizer (boron epoxy) in 1969. Since 1970, tructural

composites have been used on U.S. ighter and attack aircraft for empennage and

wing covers. The AV-8B aircraft has its wing and much of its fuselage (some 28

percent of the structural weight) made of composite material. Many aircraft of

foreign design make extensive use of organic composites.

The early aircraft employed boron-epoxy materials. This material gave way

to graphite-epoxy materials because of costs and improved design latitude. Thelower weights possible have been translated into smaller, lighter, less expensive,

higher-performing aircraft. For the same payloads, studies show tha t with about 70

percent of the structural weight in composites there can be a 22 percent reduction in

takeoff gross weight compared with a metal aircraft. However, in advanced fighter

and attack (high-performance) aircraft, two issues restrain broad use of composite

materials: affordability and the ability to operate at high (elevated) temperatures.

For these expensive aircraft, the high cost of materials is less of a deterrent to

their use than for less expensive aircraft. Even so, material costs (which can be 10

to 15 percent of the airframe cost) are not significant. Compared with aluminum,

titanium and the organic epoxies are some 8 to 10 times more expensive. In additionto the costs of materials, the cost of design, production, tes t, and certification must

be factored into the total cost of an aircraft. In general, these are more expensive

activities for composite than for metal aircraft, with the possible exceptions of

assembly, maintenance, and operations support.

The cost of most high-performance aircraft has held steady in total fly-away

price, in constant dollars, but have increased in dollars per pound empty weight.

However, the price is too high and may well stay high at the low production rates

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experienced this past decade. The question raised with regard to low production

is: if a surge in production is needed to respond to an emergency, what are the

implications for composite material production and application?

A major effort is required to quantify and reduce costs associated with composite

materials, i.e., innovative designs for automation, low-cost manufacturing, quality

assurance of material, manufactured parts and systems, and improved reproducibil-ity and repairability. Tool design and quality are also important.

For advanced high-performance aircraft designs, higher-temperature operations

are required. Current epoxy-matrix materials are limited to service temperatures

of 260°F.Bismaleimide and polyimide-matrix composites and metal-matrix com-

posites can be operated at higher temperatures, 550°F and 1,200°F, espectively,

but they are expensive. Ceramic-matrix composites hold out promise for operation

at up to 4,800"F with protective coatings. This arena requires considerable work

that needs to sta rt now if the conceptual supersonic and hypersonic aircraft of the

twenty-first century are to be realized. There is no question that this represents a

large future for structural composites (organic, metal, and ceramic).Current problems with the application of organic composites include: variability

of materials, processes, final geometry, and strength. Wide use of composites is

inhibited by costs, inspectibility, schedule uncertainties, risk, and investment. An-

alytical tools are not show-stoppers, but better tools will reduce cost, weight, and

development schedules and equate to improved vehicle and program performance.

The drivers for greater use of composites are weight reduction, performace im-

provement, corrosion resistance, low observability, and survivability.

Thermoplastics have a definite role in the near term for substructures and sec-

ondary structures. As for thermosets, costs need to be reduced.

Technical barriers to broader use of organic composites relate to:

0 Material variability;

0 Costs from design to certification and support;

0 Lack of dat a bases and approved specifications, standards, and

0 Inadequate cost bases for investment; and

0 Lack of confidence in new technology.

There is a need to characterize and standardize material data bases and element

testing. Analytical tools, though adequate overall, need improvement. Testing

techniques, the "building block" approach, have been adequate.The barriers to bonding relate primarily to secondary joints where there are

problems with variability of parts, fit-up, inspection, nondestructive testing, high-

temperature adhesives, and out-of-plane loads.

design allowables;

Recommended actions include:

Standardization of such factors as materials and process specification, de-

sign properties, analytics, testing techniques, certification procedures, and high-

temperature materials;

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NASA support of FAA certification activity t o develop uniform procedures

Government laboratories should do some work in material synthesis but also

sponsor industry effort;

Government should support multiple-award R&D programs and high-risk in-

novative technology developments, and should provide better mechanisms for tran-sition into production.

and ground rules;

It is projected that the next generation of high-performance aircraft will use

some 35 to 45 percent composites by weight of the airframe. A s noted, this can

be translated into smaller, lighter, less costly aircraft for a given mission compared

with an all-metal aircraft. There are no show-stoppers for service temperatures up

to 350°F (sustained speeds of M 2+). Greater use of composite materials are inhib-

ited by affordability, temperature capability (beyond 800"F), nd standardization

of materials, processes, and testing. Standardization is very important to facili-

tate communication between activities within an organization as well as betweenorganizations.

Rockwell International (L. W. ackman)

For the B-1 aircraft program, Rockwell is using composites for structures at

a rate of about 400,000pounds per year. The tooling and handling processes axe

automated to accelerate production and for consistency.

The company has invested significant contract and in-house funds to develop

da ta bases and analytical tools. A t Rockwell the composite R&D effort began in

1965 (T-39 wing box) and continued with component and test technology of a genericand specific nature up to work in 1985 on leading edges, large aircraft wings, and

B-1B components. About $100million of Rockwell and government funds has been

invested in this work. About $30 million has been invested in developinga composites

test da ta base. This involved flight certification and materials characterization work

using coupons and elements, and full-scale tests for static, fatigue, temperature,

and environment and service test conditions. The material characterization work

has resulted in the preparation of an advanced composite design guide based on

approximately 15,000 ests. Rockwell's standards and allowable design strain levels

for composites are incorporated in this design handbook.

The B-1B composite components (flap, wing pivot fairing, rotary launcher,weapons bay door, and wing movable fairing among others) have undergone stat ic

and fatigue tests.

Rockwell has on-hand many of the computer programs needed for composite

applications analysis. They were generated by Rockwell and others and cover such

matters as: point stress; bonded symmetric-stepped laminate characterization; mois-

ture absorption; design-stiffened, skin plate, wide column optimization; aeroelastic

tailoring; and structural optimization.

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Standard ultrasonic and x-ray as well as "coin tap" and visual nondestructive-

testing techniques are used to validate manufactured articles. However, these tech-

niques are not suitable for thick or complex structures. The latter require (undesir-

able) hatches and holes that still may not provide appropriate access.

A building-block approach to certification is used that covers the issues of lifetime

prediction and accelerated testing. A key to this approach is for each building block

to have the same type of failure mode as the blocks grow in complexity.

Because of the benefits associated with all bonded structures-structural in-

tegrity, lower weight (about 10 percent), lower manufacturing cost (about 15 per-

cent), and reduced fuel leakage-Rockwell is committed to bonded, integral compos-

ite wings for future aircraft. Design must consider inspection, damage containment,

bat tle damage, and production rate and supportability.

Experience has shown these matters to be problems: out-of-plane loads-difficult

to predict, need good modeling; effectsof impact damage on compressive strength-

an empirical process, need better analytical tools; environmental effects-though

generally understood, need careful design attention; bearing interaction allowablestrength-tools for analyses reasonably in hand; bonded-joint thermal mismatch-a

serious issue in need of at ent ion; variability of bonded-joint quality-design ap-

proaches and validation techniques needed; and durability and damage tolerance

prediction-a real problem, need prediction techniques since analytical tools are not

available and designers are forced to depend upon testing.

The factors that inhibit wider use of composites include: initial acquisition costs

of tooling; limited service temperatures; integrity of bonded primary structure oints;

areas of high-load transfer-designers use metals since they handle concentrated

loads better; supportability requirements-difficult to identify and estimate costs

since good models are not available; sensitivity to low-level impact damage; andeffects of hostile threats, such as from lasers-need to be examined. Also of concern

are tools to allow reasonable analyses of flaw growth and life prediction, postbuckling

failure characteristics, and out-of-plane strength prediction.

The factors stimulating interest in composites are: lower weight and cost (15

to 25 percent versus metallics); lower part counts; aeroelastic tailoring; and re-

duced radar signature. Full appreciation of composites will come only with design

approaches that do not follow metal practices by making best use of composite

characteristics.

There is a place for thermoplastics but more technology development is needed.

If they are to be used for high-temperature applications, new materials are needed.

It would be very desirable to characterize, across the industry, the material data

base. There is a need to s tart now to standardize specifications and test procedures.

This needs to be accompanied by standardized procurement, processing, and testing

specifications. There would be a real payoff with this activity.

Technical barriers to the application of composites include the establishment

of out-of-plane failure criteria and improved methods of analyzing joint-load distri-

bution, and techniques for testing impact effects, bat tle damage, and standardized

specimens.

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For adhesive bonding, the major technical barriers are considered to be design

confidence, thermal mismatch, and surface preparation requirements. These can

be resolved through additional PABST-type programs with elevated temperature

(350°F) aterials, use of lower thermal expansion materials when bonding metals

to composites, and improved process control.

It is recommended that the government continue to play a key role in enhancingthe technology data base where there is high risk associated with new materials

and manufacturing techniques, in developing the technology prior to production

application, and in transferring technology. Government and industrial teaming is

a good way to build the data base and transfer the technology. In this regard, it

is important that the DOD also give attention t o the technology transfer problem.

Here, technology transfer meetings and teaming will be of real help. Continued

university involvement is encouraged.

The development of professionals for this growing area would be helped by

expanding university commitment and participation, increasing company-sponsored

training, and using professional societies for such matters as setting standards andtest procedures.

Lockheed Corporation (J. B. Hammond)

For the 199Os, here will be a mix of metals and composites. A systems look at

design is required t o get the best mix for maximized fleet effectiveness. However,

there will be a high percentage of organic composites, with metals in appropriate

places, approaching 50 percent by weight and providing some 20 to 25 percent

structural weight reduction.

The nature of the future factory will change. With the move from aluminum

structures to current composites, there was an ncrease in attention to materials andfabrication. With more advances in composite applications, attention to materials

will increaseaswill attention to assembly, particularly to material quality and quality

control, and automation. The factory will handle a mix of materials: composites,titanium, and advanced aluminum. This will tend to increase factory complexity

and costs. However, it is believed that composite structure fabrication and labor

cost-saving techniques can result in an airplane with significant composite content

th at will have costs equal to that of an equivalent all-metal aircraft.

Carbon-fiber-reinforced matrix system program drivers are thermoplastic sys-

tems for up to 350°F to 450"F, igh modulus/strain fibers and tough epoxies,

and high-temperature systems. The higher-temperature thermoplastics promise lowmanufacturing costs and supportability improvements, but technology readiness re-

quires significant additional effort. A possible, important composite design problem

relates to the ability to handle cyclic loads.

Work shows that cooling rates for thermoplastics can have significant effects on

material characteristics and can be used to modify materially the characteristics.

Thus, more work to develop a fundamental understanding of material parameters

and their influence on processing and finished-part structural behavior is indicated.

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Variables include fiber type, pretreatment and degree of bridging, thermal cycling,

processing, and interphase morphology.

Thermoplastics will require barriers for fuel containment but this can be handled.

Thermoplastics are of interest for reasons other than relative ease of formability.

They are reformable, can be fused and welded, and waste material can be reused.

To take advantage of these characteristics, however, will require work to increasetoughness and manufacturing flexibility and to reduce costs.

The technology development needs for both thermosets and thermoplastics in-

clude tough high-temperature resin systems that are compatible with high modu-

lus/strain fibers, can be automated, and can be cost-effective. Thermoplastic tech-

nology development needs to encompass optimal resins, surface-coating adhesion

and adhesives, development of qualification test parameters, and identification of

low-cost manufacturing processes.

The basic composites issue is the ability to get low-cost structures that satisfy

system performance requirements. Accelerating the development of thermoplastic

technology with emphasis on costs and productivity would help achieve this. In gen-eral, there is a need for better, common-specification analysis and test methodology,

and methods for handling out-of-plane loads. NASA should pursue this basic work.

McDonnell Douglas Corporation (E. D. Bouchard)

McDonnell Douglas has a major commitment to use composite materials. With

these materials, it has been possible to contain aircraft structural weight while

meeting more demanding performance and supportability requirements on the F-15

(Eagle), F-18 (Hornet) , and AV-8B (Harrier 11) aircraft. The composite structuralweights of the F-15, F-18, and AV-8B are 1 ,9 , and 26 percent, while the number of

composite parts and assemblies vary from 16/7 to 145/59 to 502/25, respectively.

The estimated structural weight savings are F-15,24 percent, and F-18,18 percent.

For the F-15, the major composite applied is boron epoxy for the vertical and hori-

zontal tail torque boxes. Carbon epoxy is used for the majority of other composite

parts. Carbon bismaleimide is used to a limited extent in the AV-8B aircraft. The

rest of the composites are carbon epoxy. To date, over 90,000 detailed parts and

30,000 assemblies have been delivered for service aircraft.

Sophisticated analytical techniques are required for successful development of

design features such as wing root joints, cutouts, local hot spots, and wing skins.

Critical areas require extremely fine grid modeling.

The key to expanded use of composites and exploitation of higher-strain levels

is the continued development of analytical tools that include automated design and

analysis methodology.

As noted, organic composites are used extensively on AV-8B aircraft. Thisincludes carbon epoxy, fiberglass epoxy, carbon/BMI, and fiberglass/BMI. On this

airplane, carbon bismaleimide is used in the strakes that are exposed to the hot

exhaust gases during hovering flight. The wing skins are mechanically fastened to

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spars and ribs that are corrugated. A major portion of the wing servesas an integral

fuel tank.

concern, but is not an insurmountable problem. The success of these composite

programs depended on extensive, thorough design and preproduction testing from

parts has been and still is an area of major concern.

The McDonnell-Douglas commitment to composites will increase material de-

mand. Today, some 1,500 pounds of composite prepreg is used daily.

Experience has shown hard tooling to be a good investment. Inexpensive “soft”

tooling has resulted in serious manufacturing problems. One cost-effective, hard-

tooling concept is electroformed nickel faceplates supported by lightweight steel

frames. Though tooling can be expensive, integral molding of parts saves many

labor hours and has resulted in net cost savings.

Successful production experience requires a serious commitment to facilities and

equipment. In addition automation of manufacturing methods, inspection proce-

dures, processes, and tools are mandatory for cost reduction.

In the long-term, expanded utilization of organic composite structures offers

significant performance gains. Enhanced automation coupled with innovative design

and manufacturing approaches can provide substantial cost reductions. Government

agency support of related research and technology is considered highly desirable.

In future programs, trade studies must be performed that examine life-cycle

costs with appropriate consideration for the benefits offered by composite mate-

rials. Fatigue, environmental effect , and other operational factors are significant

considerations.

Specifically, technology needs to address high-strain/low-density fibers, tough

resin syst em , high-temperature resin systems, integrated s tructural analysis codes,improvements in adhesives, reductions in material and fabrication costs, and explo-

ration of thermoplastic potential. In this work, it is important for the government to

maintain a competitive environment and to examine competing systems, including

metals and metal matrices.

Structural testing of the composite parts has been and still is an area of major

coupons to components to structural assemblies. Structural testing of composite

Boeing Military Airplane Company (J.E. McCarty)

We will see continued, expanded application of composites to aircraft. However,

continued technology development can bring significant improvements; of particular

interest is improvement in efficiency of application. One concern is the proliferation

of new materials.

Boeing’s current programs address thermoplastics, damage tolerance, surviv-

ability, repair, analytical techniques, and manufacturing.

The Navy’s A-6 (Intruder) wing replacement program is providing valuable

experience in the application of composites (IM6/3501-6 graphite epoxy). The wing,

a primary structure, is of typical multispar construction with a wing fold mechanism.

Thermoplastics work for the Air Force concentrates on polyetheretherketone

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(PEEK) nd high-temperature materials, and will result in the fabrication and flight

of a flap on an A-10 (Thunderbolt) aircraft. The materials used will be characterized,

but this will not constitute a material data-base program.

The R&D work on damage tolerance includes development of a set of require-

ments for Air Force aircraft, an assessment of analyses for flight safety critical-

damage evaluations, and development of analyses for assessing impact damage andresulting residual strength. In support of this work, a multispar rib box is being

constructed for testing.

Thermoplastics is a key effort at Boeing. The interest in thermoplastics is

twofold-higher toughness and the potential for lower costs. Special emphasis is

directed at high-temperature systems with special interest in material forms, resin-

based failure, processing, and through-the-thickness analysis including impact dam-

age and effects.

Analysis capability is considered important and is being pursued. A t present,

ply properties are used to establish laminate modulus and testing, to define failure

strains or stresses and allowables at the laminate level.A good data base has been established on the following thermosets: primary

structure 350°F cure graphite epoxy AS4/3501-6, T-300/934, T-300/5208, and

IM6/3501-6.A larger data base is needed for thermosets. This will be developed

once material is selected.

Because of the commitment to composites, there is a significant effort focused

on expanding the use of organic composites. This expansion is through attention to

materials, design and analysis, and manufacture and quality control.

Regarding materials, there has been significant improvements in fiber-strain and

failure capability. These are important matters to pursue because of the favorable

impact they have on weight, design flexibility, and cost. Improvements in resintoughness are also important. A better understanding of fiber-resin interfaces is

needed to take full advantage of component improvement.

An important aspect of the cost issue is manufacturing tolerance. A broadening

of tolerances will be reflected in reduced costs. Standardization of materials and

processes including testing could help considerably in cost reductions. Industry

should collectively address these matters.

In design and analysis, as has been noted, the following need more attention:

through-the-thickness analysis, residual strength after impacts, and resin-dominated

load paths. Increased effort is also required to provide the tools for addressing

multimode failure, interlaminar allowables, the modeling of secondary loads, and life

prediction. Regarding life prediction, there is essentially no capability a t all; special

attention is needed now.

There will be a high payoff in manufacturing and quality assurance if attention

is given to: lay-up automation, preprocessing control (checks before problems and

errors are built-in), postprocessing inspection, standardization (especially for clips

and brackets, where there is a potentially large business), and allowance for some

reforming of components to fit varying designs. All of this will help cost reduction.

The matters tha t inhibit fuller use of organic composites include: labor, material,

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and facility costs; the costs of obtaining and maintaining adequate da ta bases; the

costs of compliance to specifications and certification; the brittle nature of the

materials and sensitivity to damage; and the shortage of experienced and qualified

engineering and shop personnel.

Honeycomb is a good design concept but it acquired a bad reputation. DOD

has taken the position that it should be avoided. What is needed is a good design-acceptance criterion.

The government has an important and significant role in accelerating the uti-

lization of organic composites. There are two aspects to this support: (1)high-risk,

long-term technology developments (i.e., thermoplastics, innovation, and program

acceleration), and (2) technology transfer (i.e., more focus on collection and ex-

change of data at the macro and micro levels). This is not effectively accomplished

today. Two specific questions related to bonding need to be addressed: What is a

strong bond? and How can wide-area bond separation be detected?

The government should, as part of its activity, support basic technology im-

provements in analytics, materials, manufacturing (including process impacts), andquality assurance methods aswell as data-base development and standardization es-

pecially for new, developing materials and their fabrication techniques. MIL Hand-

book 17 provides a good st ar t on a da ta base. Industry should support this effort.

In summary, the fundamental tools for design exist, but they need improvement

to allow full utilization of the inherent characteristics of composites. Often problems

are “designed around” rather than resolved because of the lack of the ability to

understand and handle them. For preliminary design, “quick” design tools would be

very helpful. Cost is a major deterrent to expanded use of organic composites. What

is needed is continued development of the technology across the board to maximize

utility and reduce costs.

General Dynamics (C. F. Herndon)

The principal issue being addressed is composite material toughness for next-

generation, high-performance aircraft. These aircraft may well see composite struc-

tural weights in the range of 4‘0 to 60 percent of the total structural weight. However,

some current materials are too fragile for economical handling and processing. Fu-

ture growth in the application of composites for high-performance aircraft depends

on material developments and processing that result in tougher s tructural systems.

Experience from the 1970s and 1980shas proven the role of composites in high-

performance aircraft. The question is the degree of their further practical applica-tion.

General Dynamics, in its application of composites, has had extensive, success-

ful experience on the F-16 (Falcon-l,600 ship sets manufactured and 1,500 aircraft

delivered). Over 1million flight hours have been accumulated on this aircraft, with

some having flown in the 1,000 to 2,000 hour range. The vertical stabilizers on these

aircraft use thick, relatively flat laminates tha t are blind riveted to aluminum struc-

tures with bonded graphite spars and graphite laminate skins, and rudders made of

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honeycomb cores with bonded graphite laminate skins and aluminum spars and ribs.

The horizontal stabilizers use replaceable leading edges, as is used above, with cor-

rugated aluminum substructure and riveted laminate skins with an aluminum root

rib and shaft. The F-16 composite application has been simple and conservative.

The present composite systems have many limitations: they are susceptible

to edge delamination; hole drilling and fasteners must be handled with great care

to avoid local damage; and the systems are vulnerable to impacts. It is expected

that next-generation aircraft will have more extensive composite application (4 0

percent to 60 percent) and be more complex. They will cover the exterior of the

aircraft and be applied selectively for substructure. High-modulus fibers will be

used. The contours will be complex and made from thin materials. Fuel tanks

will use composites. The aircraft will require temperature-tolerant composites for

operation at greater than M = 2.The future technology thrusts need to be toward toughness for thin skins and

larger panels to allow easier repair and maintenance and improved warranties.

Toughness has not been easy to define because of design variables, the nature ofdamage, and the detectability of damage. The toughness issue is further compli-

cated by the demands of manufacturing processes for flexibility, tolerance, and ease

of manufacturing, including the ease of drilling, fastening, mating, and avoidance of

local failures in forming.

Material properties t ha t contribute to tough properties are strain critical energy

release rates (Glc and Grrc), edge delamination strength (EDS), and incipient

impact energy (1IE)-a set of interrelated properties. The test techniques used for

determining these parameters do not, in most cases, represent real structures and

thus do not always correlate well with full-scale test data. This issue needs to be

examined.An examination of where the technology stands and what is wanted regarding

toughness indicates that the desired levels of toughness can be achieved. Ther-

moplastics have a role here. Proposed material properties are identified in Table

A-2. In addition, the new materials need to have chemical resistance, repeatable

processibility, machinability, lightning-strike compatibility, uniformity, and fatigue

resistance.

In summary, experience to date is good but cannot be extrapolated; current

materials are not good enough for projected high-performance aircraft; the nature

of damage sources and progression needs to be identified; work needs to be directed

at defining material properties that provide a good measure of toughness; and effort

needs to be put into the development of tough composite materials-new thermosets

may succeed and thermoplastics show promise.

The future for organic-matrix composites is bright. The factors that drive the

interest in them are weight savings (performance gains), reduced part counts, re-

duced assembly time, corrosion resistance, and long fatigue life. A major obstacle is

low tolerance to damage. Government and industry should place great emphasis on

removing this obstacle.

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TABLE A-2 C r i t i c a l M a t e r i a l P r o p e r t i e s P r o p o s e d f o rH i g h - T e m p e r a t u r e C o m p o s it e s

P r o p e r t y

C u r r e n tM a t e r i a 1

Sys t em

N e a r - T e r m T a r g e tM a t e r i a 1

Sys t em Sys t em

M a t er i a l

E ] ] (Yo) 1.1 1.3 1.3

E l 1 (MSI) 19.6 24.5 24.5

G I 2 ( H O T / W E T ) (M S I) 0.35 0.35 0.35

TG ( W E T ) O F 350.0 325.0 350.0

p (lb/in’) 0.058 0.058 0.058

0.6 3.8 8.0

1 o 3.8 12.0

EDS ( K Si ) 28.0 35.0 120.0

I I E ( f t - l b / i n ) 20.0 40.0 150.0

G I c ( i n - l b / i n 2)

GIIc ( i n - l b / i n 2)

S O U R C E : G e n e r a l D y n a m i c C o r p o r a t i o n , 19 86 .

Northrop Corporation (R. S. Whitehead)

Designing with graphite composites does not present large, unsolvable prob-

lems. There have been 20 years of experience in their application. Their structural

efficiency, atigue resistance, and ability to withstand corrosion have been demon-

strated. The technical problems are surmountable. Technical design matters and

certification issues are understood and basically manageable.

The general experience is that composite parts are more expensive (per pound)

to produce than aluminum and supportability of composite structures is poor. This

aspect of design needs more attention.

With careful design, some of the critical certification issues can be resolved, Le.,

temperature and moisture effects, material selection, fatigue and corrosion resis-

tance, accelerated testing, and certification. However, work on the following matters

is needed and very appropriate: out-of-plane failure modes, predication of full-scale

structural performance, service durability of thin structures, and methodology to

assess damage tolerance.

The matter of full-scale structural performance is especially worrisome. Most

often, problems are not anticipated or understood until full-scale, complete aircraft

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testing is accomplished. This applies to all classes of aircraft and is reflected in the

fact that a significant number of full-scale test articles have failed (below design

ultimate load) because of unanticipated failure modes. The major cause of these

unanticipated failures have been out-of-plane loads. Analytical methodology is a

vital need in this area. Of significant help would be dissemination of lessons learned

from full-scale testing.

Northrop’s experience in the production of F-18 (Hornet) vertical stabilizers

(graphite epoxy) and F-5 (Tiger) stabilizers, when normalized, shows that the

composite component is less costly than the aluminum structure ($14,700 versus

$18,700). Composite material costs are greater ($37/pound versus $3/pound), but

only 103 pounds, versus 135 pounds, of composite materials are used and labor hours

are 90 for composites versus 158 for aluminum. These factors make a significant dif-

ference.

In addition to the high potential for reduced manufacturing costs, life-cycle costs

should be reduced too. Cost reductions should accrue through lower weight, smaller

aircraft, higher performance, excellent fatigue and corrosion resistance, and repairsimplicity. However, the forenoted thin structures present problems related to edge

damage, impact dents, punctures, handling damage, and moisture absorption. Lack

of paint adherence is another annoying problem.

Future technology development with the potential for high returns are: im-

proved manufacturing techniques to reduce acquisition costs; the improvement in

operational maintainability and supportability (especially for thin surfaces) to im-

prove operational readiness and lower life-cycle costs; and dissemination of lessons

learned within the industry to minimize design and test process development redun-

dancy. The government can be of considerable help here. NASA could do this job

effectively.

Business Aircraft

Beech Aircraft (R . Abbott)

The health of the general aviation industry in the 19809, compared with the

19709, is poor both in number of units delivered and dollars of sales, especially when

discounted for inflation. The pressure is on for industry to bring forth new high-

performing products at reasonable prices. This is a matter of survival. Composites

will play an important role.

The Beech Starship1 is a response to this business condition. It represents a

$240 million investment. By late 1986, production buildup is projected to cost $7

million per week. The aircraft structure will be about 70 percent composites (about

2,600 pounds of stiffened-skin composite construction).

The tools and facilities used for construction are adequate for conventional

prepreg and autoclave application but cause high costs. Lower cost methods would

be employed more extensively (resin injection, pultrusion, and filament winding) but

for the lack of facilities and processes and of resources for their development.

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The analytical tools used are considered adequate for design (laminate and finite

element methods) but need refinement for certification work (laminate stability

modes, very fine grid for local effects, and delamination). One matter of special

significance is that current fatigue life analyses are not acceptable to the FAA.

Other technical matters requiring attention include durability, environmenta1effects,

variability, material stability, and defects including delamination.The present data bases are not fully adequate for new designs. FAA circular

AC20-107A (paragraph 6, page 3 and paragraph 7, page 4) illustrates the need for

detailed attention to analytical tools to help minimize expensive, time-consuming,

full-scale testing for certification. Published data bases (i.e., static and flaw growth

compression and design strain-limit compression) are used for design followed by

explicit company tests of materials under a range of environmental and damage

conditions.

Adhesive bonding is employed for the wing. Bonding was chosen based on loads,

allowables, weight, costs, and maintainability. Woven joint sections are used to

bond skins to spars. High-load points are bonded and bolted through titanium andaluminum fittings.

Certification issues involve: damage detectability and damage-related ultimate-

load design requirements; flaw growth and the scatter/threshold of stress; selection

of environmental criteria for durability tests; proven techniques for laminate failure

analyses; and quality assurance and safety of bonded joints. Beech has been involved

in a dialog with the FAA regarding the documentation of material for the certification

of bonded structures and their tolerance to flaws, environmental effects, and damage.

It is expected that at production rates, 18,000 pounds of graphite epoxy will be

used per month. In more advanced designs, the material may not be graphite.

Work to date shows that: compression members are designed by the threshold

of impact damage detectability (resulting in the lowering of operational stress levels

to n-growth) ; “tool-proof” wing tests provide very useful data (compression stress

concentrations, spar discontinuity, and incomplete torsion load path) ;and wet lay-up

repairs during testing allow continued tests up to the point of failure.

When comparing composites with metals, experience shows that sta tic compres-

sion (for damaged components) is critical compared to tension and fatigue, and that

there is much greater scatter in flaw growth and life.

As others have found, composites have these advantages: lower airframe part

count (King Air, approximately 8,000; Starship, approximately 1,700); lower cost

and improved capability to tailor properties; lower weight; better contour control;

and no corrosion. However, there are serious inhibitors to wider use: cost of man-ufacturing; lightning and related electromagnetic effects; certification cost and risk;

and low bearing strength. Regarding manufacturing costs, labor is approximately

$4 per pound at present. Effort is directed at getting it to $2 per pound.

The technical barriers to wider use of organic composites center around corre-

lation to analysis, data variability, flaw growth, environmental tests and methods,

and professional staffing.

Laminate analyses predict elastic properties, but they are inadequate for first

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ply failure prediction of allowables of loads and stress because of material variability.

Finite element analysis predicts strain and deflection but does not predict failure

load, stability, or stress concentrations, nor does it handle incomplete load paths.

However, the situation is about the same for metals.

Currently, static testing shows considerable scatter between lamina and laminate

data. Durability testing requirements are uncertain. At present, test loads are

designed to achieve two test lives. It is considered that this is equal to one service

life. The FAA recommends and requires a statistically significant number of load

cycles, but how many cycles is this? A B-basis at lo7 cycles is used for threshold

stress.

With regard to environmental testing, although present techniques are adequate

they are time consuming and costly because of the large test matrix and the require-

ment for proof of thermal and moisture structural strain.

Adhesive bonding methods are available and have been successfully applied to

joints, but it is clear from experience that surface preparation, quality assurance

checks, and manufacturing care are needed. A t Beech, a water break test is usedfor quality assurance of surface preparation. FAA has noted th at it would prefer a

direct method for checking the strength of each bond after processing.

General aviation has found it difficult to find individuals with combined aircraft

design and composites skills. Most often the industry resorts to the hiring and

training of new graduates. But when business is down, these people often are lost to

the large, prime companies.

In summary, technology development is needed in areas related to manufac-

turing, analysis, and certification. In manufacturing, inexpensive methods for pro-

ducing small composite parts (clips, brackets, and castings) to replace metal parts

would be very useful. Stress on thermoplastics is needed to help clarify its placeand value in future designs. Joint NASA/DOD effort in manufacturing technology

development in these and other areas can have a large payoff.

Work on analysis methods, too, will have real payoff. Development of methods

(and a handbook) addressing failure modes would be of specific value, i.e., stability,

first ply failure, bearing strength, and flaw growth. Material characterization is an

integral part of this effort and may well be the major issue. Joint sponsorship of

university work by NASA and DOD is indicated.

Finally, regarding certification, damage tolerance guidelines for bonded struc-

tures are needed. The issuance of an advisory circular developed jointly by FAA and

industry would be very useful.

Gulfstream American (H . Wardell)

The drive to composites for the GulfstreamIVwas weight reduction. The aircraft

has a typical metal s tructure with floor panels manufactured in-house and the fol-

lowing parts manufactured by others: rudder, ailerons, spoilers, wing trailing edges,

forward and aft wing-body fairings, (nonpressurized) floor panels, horizont a1 and

vertical stabilizer overhang panels, pressure bulkhead panels and beams, pylon ribs

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and covers, and nacelle doors and fixed cowls. In time, most of this manufacturing

will be moved in-house.

From this multiple exposure to composite designers and producers, it is painfully

clear that no two parties do things alike. This has produced many problems from

specification to acceptance testing for Gulfstream. All parties are aghast at what

the others do:

Require a minimum percentage of 90" plies versus no requirement.

Re-cure versus ce cure of honeycomb skins.

Redrying versus no drying of Nomex core.

Tool selection variations, Le., nickel, composite, aluminum, and matched dies.

Requirements versus no requirements for environmental control.

0 Kevlar considered a moisture barrier versus a moisture trap.

It was found that if designers did not work with the manufacturing groups it was

necessary to redesign for manufacturing.

Gulfstream is building a composites facility (70,000 square feet-a $6 millioninvestment). The facility will have a bond room, autoclave room, quality control

laboratory, a nondestructive-test section, and a tr im room with appropriate current

equipment for projected work. The composite activity has a staff of 60 that is

projected to grow to 244 by mid-1987.

A t present, for preliminary design, available industry data bases and analytical

techniques are used. Tests to one lifetime are made in conformance with FAA AC

20-107A for primary s tructural lay-ups with maximum nondetectable damage.

The following are considered problem and inhibiting factors to broader use of

composites:

0 Lightning protection and knowledge related to expected damage and effectivepreventive design methods.

0 Nomex core-environmental control requirements and their minimization.

0 Honeycomb panels with 45" bevel angles failed much before panels with 25"

Aluminum-core graphite-epoxy pans deformed in secondary bonding cycles

0 Parts inspected and passed by vendor or manufacturer being rejected by

0 Identification of the best standard test procedures and knowing or under-

The need for the individual manufacturer to identify material allowables for

0 Identification of an acceptable corrosion barrier.

0 No industry-wide set of composite fastener lists.

A t Gulfstream, the lack of data bases on defects for such things as porosity,

delamination, voids, and ply wrinkles inhibit wider use of composites. These factors

directly impact production rate and cost. Another important fact, vendors and

bevels.

due to thermal mismatch (Nomex did not).

another even when inspected to same specification.

standing what the results reveal.

specific systems and specifications.

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outfitters lack the knowledge required to handle composites properly. Much more

care is required than for metals in protecting the integrity of the aircraft when

drilling for things such as mountings, attachment clips, and brackets for out-of-plant

modifications.

The field could be helped by having: data readily available on manufacturing

discrepancies (a comprehensive research effort quantifying effects, paralleling what

is done for metals, would be helpful); feasibility studies for primary, intermediate,

and nonstructural parts for varying design stra in rates; studies of hole tolerance on

fatigue strength; and studies to identify design strain parameters and values.

The larger companies can gather this class of data. The smaller companies are

hard put to do the same. Yet, these kinds of data are required before a company can

commit to full application of composites with low risk.

Airlines

Trans World Airlines (J. Janas)These remarks relate to operational maintenance and experience, not design.

Trans World Airlines (TWA) has had experience with composites on the 727 air-

craft. Ultrasonic tests are used to check for debonding. Water ingestion is a com-

mon, relatively serious problem if the design is not proper. It leads to delamination,

crushed cores, and out-of-balance trim conditions in flight. Other operating prob-

lems relate to the effects of oil and hydraulic fluid contamination and corrosion

on struc tural integrity. TWA has also experienced delamination in noses of engine

cowlings associated with the operating environment.

“Battle damage” is another general problem in civil operations. It is associated

with ground crews, equipment, jet ways, hail, and other operational causes. Damagecan be serious and costly to repair.

In general, there is low confidence in honeycomb because of water ingestion.

There is also some concern about the crazing and cracking of Kevlar and associated

structural integrity implications. Of special note is the need to replace about 60

windows per month on 747 aircraft because of crazing.

In the area of repair, temporary, airworthy repairs would be of great help. The

ability to fly the aircraft back to the dedicated repair base or to continue in-service

for limited periods can save an airline significant funds.

Nondestructive-testing techniques are needed to evaluate damage. For low-

power x-ray equipment, there is a need to better understand what is seen on the

picture and what it means. Airline operators need significant help in composite

repair and maintenance.

Material Suppliers

Ferro Corporation (D. Forest)

Today the composite market for aircraft is dominated by fiber-woven fabrics,

tapes, and rovings impregnated with resin. Good business da ta on the industry are

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T A B L E A -3 Co mp o s i t e M ate r i a l Bu s in ess P ro j ec t i o n

1977 1985 1990

Sales , $m i l l ionIn v es tmen t , $ mi l l i o nT o t a l e m p l o y e e sP ro fess io n a l sM a j o r c o m p e t i to r s , w o r l d w i d eN u m b e r o f p r o d u c t s ( a p p r o x i m a t e )L o t s iz e , a v e r a g e p o u n d sM a r k e t g r o w t h , a n n u a l p e r c e n t a g eP r o d u c t i o n c a p a c i t y , p o u n d s (m i l l io n )

Wo v en p rep regH o t - m e l t t a p e

R o v i n gC a p a c i t y u t i l i z a t i o n , p e r c e n t

8 020

1,00040 0

8100200

20

1 331

60

350400

2,6009 0 0

201,000

1 001 5

18.57.7

2.035

1,000650

5,000

2,00010

10,0001,000

10

3015

570

S O U R C E : F e r r o C o r p o r a t i o n , 1 98 6.

not available, but within f 20 percent, it is believed they can be characterized by

estimates in Table A-3.

The market is relatively small, $350 million, compared with the estimated value

of the composite components generated, $3billion. Pertinent t o the committee is the

fact tha t an average of 3 to 5 percent of sales, some $11million to $18million in 1985,

is applied to R&D by the material suppliers. Of this R&D, 70 percent is probablyspent on direct product development. This leaves$3.3million to $5.4million for new

product development. It seem clear that additional R&D investment is desirable

from government and industry sources.

The number of products has grown and is projected to continue to grow; an

effort is needed to reduce it. Profits in the business have been elusive and few

firms have a return on capital investment of over 15 percent, not a particularly

encouraging picture. Average pretax returns are about 5 percent. This low return

can be expected to reduce the number of firms in the material supply business and

can be expected to result in the development of fuller lines of activity within the

remaining firms in the longer term.From technology considerations, the user community has driven material per-

formance up, i.e., stiffness, strength, toughness, and environmental resistance.

Presently, these characteristics are considered good to excellent. Costs are low,

relatively, for the materials used, especially if the lowest-cost material form is em-

ployed for a given job and is a small portion of the end-item cost. Quality from the

consideration of reproducibility, tolerances, and material defects is a problem. Pro-

cesses need to be statistically controlled. With adequate attention to detail, this can

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be done; i.e., reduce costs of labor, rework and rejects, improve ability to automate

user processes, and improve end-product performance reliability and durability.

Today most composite applications in aircraft are thermosets. It is projected

that by the early 1990s thermoplastics will show a 20 to 30 percent utilization if:

polymers are perfected that have a high level of toughness; prices are down from the

$100 o $150per-pound level to the $15 to $20 per-pound level; and high qualityprepreg forms are developed. High cost may be the ultimate stumbling block.

Considerable development of equipment and techniques is also required to bring

the thermoplastics state of technology up to that of thermosets. A possible hindrance

is the large capital investment for materials processing required by manufacturers

to utilize thermoplastics.

The costs of prepreg materials (fibers and resins) are 50 to 60percent of the selling

price. These costs are rising at 4 to 6 percent per year. Energy (for the incineration

of polluting materials) is, at present, a major cost that can be reduced. The cost of

obtaining and maintaining quality is high. Small lot sizes add to costs. Automation

of production and quality control should help reduce material production costs aswell as end-product costs.

Through positive action on these matters, prepreg prices should move down in

the longer term. Actions to help assure that this happens include development ofcontrol laws and sensors for material processing and investment in new or improved

processing and production equipment. The end user will have to be aware of and

knowledgeable about the actions taken t o have confidence in the product delivered

and in how to use it. This will probably require sharing of data and work, matters

not easily accomplished in a competitive environment.

It is important to note tha t there is excess material production capacity world-

wide. If the need should arise, it should be relatively easy to increase capacity.

Generally, the industry works one shift; it could work two. Further increases incapacity could take about a year, requiring the manufacture and installation of new

equipment for material production.

In summary, it is recommended that: the government (NASA and others) con-

tinue t o sponsor and/or conduct polymer research and technology development; the

government continue to sponsor work to eliminate application barriers (proof-of-

concept and demonstration programs) through teams/consortiums with matching

industry funds; the government, principally DOD, support productivity improve-

ment technology through industry consortiums and, in addition, permit the early

recovery of plant and equipment investments; and universities give attention to

teaching composite design and manufacturing and give industrial engineers creden-tials in composite process control and automation.

Union Carbide (T. W . Longmire, presented by C. Trulson)

Resins are a limiting factor in composites. Problems relate to control, testing,

and qualification. There is a clear need for further intercourse and education among

suppliers, designers, and fabricators.

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Unlike metal systems, composites exhibit a broad range of properties that both

complicate and make more flexible the attack on design problems. In composite

aircraft, the struc tural characteristics of a final par t or component depend not

only on the material but also the manufacturing process. This interaction must be

carefully factored into design and testing.

Experience shows that the qualification of a new prepreg material consistingof an approved resin and a new fiber takes some 9 months and costs an estimated

$60,000. Where the new prepreg is composed of a new resin and approved fiber, it is

estimated tha t 20months and $1million are needed.

There are four general issues from the suppliers’ point of view: (1) test stan-

dardization, (2 ) prepreg standardization, (3) the use of thermoplastic matrices, and

(4 ) education and communications.

Regarding tes t standardization, the material supplier is responsible for supplies

that meet certain standards and tests to demonstrate to the user that the standards

are met. Each user has his own standards. Standardization, among users, of sample

preparation, testing, and data reduction would help reduce the number of testsrequired and speed the development of a common data base. The result should be

to reduce costs for design and production and to reduce time for response to design

requirements.

Because of the influence of manufacturing on component and system perfor-

mance, unique component and system tests will still be required. But, even here

there may be two test groupings: those that are essentially common between many

applications and those unique to a given aircraft component and system. It would be

helpful if the common testing were done by a qualified, mutually acceptable labora-

tory. This should accelerate the whole process of acceptance, design, manufacture,

and application of common parts. The government could play an active role in

the process through setting standards for specification and testing and publication

of data bases, i.e., MIL Handbook 17, and the work of the Institute for Defense

Analysis/American Society for Testing Materials (IDA/ASTM) on standard sample

preparation and testing.

In testing standardization, these matters should form the basic set of tests:

generic (unidirectional)-tensile strength and modulus, compression strengths, and

transverse properties; struc tural-element tension and compression for open holes;

and dumuge tolerance--compression after impact and edge delamination.

The prepreg standardization is an issue related to cost if cost indeed becomes a

controlling consideration. Costs could be reduced through acceptance of a standard

for prepregs in terms of width, thickness, and resin content. This would allowlonger runs and reduce expensive preparatory labor per run. This would also reduce

the amount of testing and scrap associated with start-up and shutdown. Prepreg

standardization is an issue being addressed by industrial groups.

Broader use of thermoplastics hinges on increasing material toughness. It is rea-

sonably evident tha t toughness can be improved by possibly an order of magnitude.

For broad application, two issues need to be resolved: solvent resistance and fabri-

cation technology. Both require active attention. For the first issue, requirements,

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standards, and test procedures need to be established. For the second, as for ther-

mosets, there is a need to move toward standardization of materials and material

forms. If thermoplastics are to see early application, these matters need the early

joint attention of suppliers and users. At present, 200°F to 300°F thermoplastic

systems are practical but higher-temperature systems are probably not.

As has been noted, because of the influence of manufacturing on the characteris-tics of composite parts and systems, close communication between material suppliers

and the user is needed. “Lightly structured” manufacturing technology programs

could serve to accelerate innovative manufacturing technology development through

joint supplier-manufacturer activity and produce the design data and handbooks

required to extend and accelerate the application of composites. “Perhaps we would

all know why bonded structures are held together by rivets.”

Hercules (J. N. Burns)

It is projected tha t the strength of organic composites will continue to improve.Up until 1980, improvements were due primarily to better production technique.

Since 1980, there has been a doubling in fiber tensile strength (400 KSI to the

800 KSI range) because of new product developments. Fiber tensile modulus has

also increased from the range of 32 to 35 MSI to 40 to 45 MSI. These increases in

performance indicate tha t it may not be wise to standardize.

Compression strength remains a problem that has not been resolved by the

industry. Here, the matrix is an important issue. Composite compression strength

has remained the same (in the 275 to 290 KSI range) while tensile properties have

improved significantly. A near-term goal is an improvement of 25 percent (to about

350KSI).The price of carbon fiber has come down from a value of $100 to $6.99 per pound

in constant 1972 dollars. In today’s dollars, the price is $20 per pound. Prices will

go down a little further but a major change is not projected. State-of-the-art carbon

fibers can be expected to stay in the $17 to $20 per pound range through 1990 with

advanced carbon fiber moving down from a range of $40 to $65 per pound to $25

to $35 per pound. The cost per unit of strength and specific modulus for advanced

composites (IM6 or IM7) should show an advantage over state-of-the-art products

such as AS4.

The future of carbon fibers is promising in terms of improvement in strength.

Carbon fiber modulus values should approach 50 MSI, and there should be reductions

in price.

Resin improvements are a major objective for both commercial and high-perfor-

mance military aircraft. Improvements in compression after impact (CAI) strength

of 2.5 times state-of-the-art epoxies are being requested by prime commercial air-

craft manufacturers. Military fighter aircraft requirements also request toughness

improvements, but service temperature requirements in the range of 350°F to 400°F

add to the difficulty of providing appropriate materials. Today’s military fighter

service temperature requirements are less than 300°F.

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In 1985,a new thermoset resin (8551-7)was introduced having a CAI strength

of 50 KSI, with a significantly reduced impact damage area. This area has gone from

3.5 square inches for 3501-6 o 0.40square inches in 8551-7with laminate damage

contained in the first three plies of the CAI coupon exposed to 1,500 n-lb/in impact.

It has also been found that 8551-7CAI strain is better in thermoplastics than

in thermosets for a range of impact energies. At 2,500 n-lb/in impact level CAIstrain is 0.7percent for IM7X/8551-7 ersus 0.6 percent for a thermoplastic versus

0.25 percent for a state-of-the-art epoxy. The 8551-7/IM7 as met the challenge of

increased toughness without lossof hot/wet 0" compression capability at 180°F hat

was typical of early at tempts to improve toughness.

Thermoset resins are meeting the toughness challenge and have an advantage

of being able to use existing manufacturing equipments and techniques at both ma-

terial supplier and aircraft manufacturing plants. The new material, in production

quantities, is estimated to cost about the same as state-of-the-art epoxy prepregs.

The graphite-fiber market for allkinds of products is projected to see a worldwide

growth of some 20 o 25 percent per year through this decade. In 1985, he market

was about 5 million pounds. The U S . share was about half of this. Currently, the

aircraft market is about 50 percent of the total U.S.market and is projected to grow

to 60percent by 1990.

Examination of the buildup of composite aircraft costs gives this relative per

pound cost breakdown: graphite fibers, $20; prepregs, $40; and structures, $200 to

$500 per pound. The place to get major payoff for cost reduction is in structures

manufacture, not direct material costs.

The challenges to continued composite application growth encompass: (1)ma-

terial advances-toughness, temperature tolerance, compression strength, and re-

duced cost; and (2) finished structure cost-material manufacturability, automated-

part manufacture, and product forms suitable for automation of processes.Particular help is needed in the area of improvement in compression strength.

Although it does not appear that basic material costs are a significant swing factor,

the mat ter deserves attention from these two standpoints: (1) material consistency

and (2) overspecification by end users.

Although thermoplastics were not specifically addressed in this commentary,

they are receiving serious attention.

E. I. Du Pont de Nemours (J. K. Lees)

New material developments are moving rapidly. Regarding carbon fibers, in-

creased stiffness and low cost are under study, as are new aramids. Compression

strength is a problem that is being diligently pursued. Thermoset toughness is also

being worked on as is a broad range of thermoplastics. Thermoplastics have their

special place. Both "sets" and "plastics" will be employed in future aircraft.

The general outlook is for finished product costs to come down because of better

fabrication techniques for materials and products and increased volumes of produc-

tion.

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There are a number of interesting thermoplastics in development: polyphenyl-

ene sulfide, polyetheret herketone polyamideimide, and polyimides and polyamides.

They are being examined in several product forms: impregnated yams, impregnated-

consolidated tapes, woven fabrics, and sheets. The selection of the best system will

depend on the applications and manufacturing processes.

Growth barriers from an application sense include: costs for qualification (as-sociated with the need to test finished structures); fabrication costs (lack of design

experience and personnel); and cost and knowledge of fabrication processes (new

materials with lack of experience, equipment, and personnel).

In general, qualification costs are a problem because of the need for large struc-

tural test specimens and limited ability to go (analytically) from material to small

test specimens to actual structures. In addition, there is a limited ability to analyze

designs for dynamic behavior and failure. A very high level of testing is dictated

by these factors and the fact that materials themselves have significant variability,

especially in their early development and production stage. Also, there is a lack

of key property knowledge. All of this is compounded by process variability. Thelack of standard and uniform test procedures also compounds the qualification cost

picture.

Fabrication costs are driven by lack of material uniformity, process control, and

material standards. In addition, costs increase through less than optimal use of

materials, possibily due to the limited fundamental understanding of the composite

materials and related design experience. The amount of off-line testing also can add

significant costs. Material costs, themselves, desire some consideration.

The introduction of thermoplastics has some of the older system problems. The

technology must be used properly for success. Hardware development costs can be

anticipated to be high and will require an integrated effort among suppliers, users,

and equipment developers. If this new system is to be successful, a fundamental

knowledge base needs to be developed.

Key to the future growth of composite application is the development of skilled

personnel. The universities are beginning to help.

Regarding growth in composite utilization, the following essential points can

be made: improve underst anding and predict ability-durability, dynamics, fatigue

and failure, and large structures when going from test specimens; improve fabrica-

tion technology-nondestructive testing, joints, and resin processing; and increase

training and education. Also of help would be designs that get away from “metal

replacement” philosophies and practices.

It is recommended that NASA and DOD

Encourage and support joint industry-academic programs that address fun-

damental scientific issues, performance predictability, and manufacturing science to

reduce time for design and qualification;

Assist in multidisciplinary programs to define and develop the technology

for efficient manufacturing systems accounting for material forms, processes, and

quality evaluation;

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0 Encourage cooperative industrial research;

Reduce direct activity on new material development but not catalytic actions

Assist in vital training and educational activity.

with industry; and

COMMITTEE MEETING OF MARCH 26,1986

Technology Needs and Budget

Table A-4 presents individual lists of the major research, technology, and de-

velopment (RT&D) needs as viewed by the government representatives. Table A-5

presents the government's budget plans for advanced organic composite R&T.

U.S.Army (J. Waller)

A program level review of work on the following rotorcraft subjects was p r e

sented:

Rotor-blade erosion protection;

Damage tolerance and durability of primary structures;

Fatigue methodology;

Design criteria and analysis;

Composite swashplate and hub design;

Advanced Composite Airframe Program (Bell and Sikorsky, addressing land-

ing gears, lightning protection, internal noise, repair and maintenance, crashworthi-

ness, and weapon interfaces);Automated blade and low-cost fuselage production;

Advanced fuselage tooling; and

0 Single-cure, tail rotor blades.

Some specific points made are:

In FY 1987 manufacturing technology activity has zero funding. It is the

intent of the Army to build more capability in-house and phaseou t contract work.

There is a need for better materials for rotor blades to withstand rain and

sand erosion.

Manufacturers usea

wide variety of methods for assessing fatigue that often

give different results. This makes comparative assessments difficult for the Army.

The same is true for damage and durability analyses.

What is needed and is to be pursued (through in-house and contract activity)

is the development of a design criteria "handbook" for rotorcraft. Issues related to

thermoplastics have to be addressed and included too.

0 Composite swashplate work is directed at a 15,000 to 20,000 pounds gross

weight rotorcraft.

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T A B L E A-5 G o v e r n m e n t A d v a n c e d O r g a n i c C o m po si te Research a n d T e c h n o lo g yP r o g r a m s

Fu nd ing ($mil lion)FY 1985 FY 1986 FY 1987 F Y 1988 FY 1989

Agency (Actual ) (P lan) (P r o j e c t i o n s)

U.S. A r m vTechnology baseM a t e ri a ls a n d m a n u f a c -

tu r ing technologyT o t a l

12.11.1

13.2

7.70.98.6

10.40.0

10.4

U.S. N a v v6.1 (Research)6.2 (Technology

development)

6 .3 (App l ied)T o t a l

0.3 0.3 0.3.25

2.0

2.3- -

2.2

2.5--

.5

1.75--

1.9

--2.2

U.S. Air ForceaResearch a n d d ev e lo p men tS u p p o r t ab i l i t yMa nu f a c t ur ng tec h nologyStructural concep ts ,

i n t eg r i t y su rv iv ab i l i t y ,a n d r e p a i r

T o t a l

7.00.2

10.3

8.30.5

9.4

6.00.9

16.5

2.319.8

2.620.8

3.426.8

F ed era l Av ia t i o nAd min i s t r a t i o n

Nondest ruct ive inspect ionFuselage damage con tain -

men tSt ructural response

crash wo r th in essT o t a l

0.1 0.1 0.1

0.1 0.1 0.4

0.1

0.30.5

1 o0.1

0.3

Nat io n a l Aero n au ti cs an dS p ace Ad m in i s t r a t io n D

Larg e s t ru c tu res p ro g ramsf u n d s

Advanced composi tes(R& T b ase)R& T b aseF Y 1987 augmentat ion

T o t a l

3.4

2.92.0

--2.43.25.6

1.93.04.9.9

"Funding does not cover salaries, metal-related work, or low observables.'Funding fo r research an d technology (R& T) on ly ; does no t includ e personn el an doverhead costs.

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0 The Advanced Composite Airframe (rotorcraft) Program (ACAP) is the first

aircraft designed to all the requirements of military standard 1290, ‘Light Fixed and

Rotor Wing Aircraft Crashworthiness.” The program indicates that a 24 percent

weight and a 24 percent cost savings over a conventional metal rotorcraft could be

realized in an order for 1,000 aircraft.

An advanced development program is under way on an advanced compositerotor hub. The rotor hub will be flight tested on an AH-64 Apache.

A single-cure tail rotor blade design is estimated to save about $700 per tail

rotor and is being placed in production by Bell.

0 Composite materials may need to be specified by the end-product buyer to

allow reasonable control over design and related operations support. At present,

each manufacturer uses the material it wants to use.

Additional Comments* The technology needs for application of composite materials

and structures for Army aviation are discussed in two categories (1) the specific

needs related to military requirements for Army aviation, and (2) technology needsfor aviation in general.

In Army aviation there are military characteristics that dictate particular re-

quirements that affect composite structural design and technology needs for materi-

als and structures. For Army aviation the needs are:

Tolerance to various levels of ballistic threats. Generally, lower-level threats

can be adequately handled in composite designs. It is high-level threats that present

the challenge for innovative design.

Tolerance to directed energy threats, both low- and high-energy, need to be

considered in the design of composite structures.

0 Repairability, maintainability, and capability are needed in adverse environ-ments. Army aircraft operate in all types of weather, day and night, under battlefield

conditions. I t will be necessary to repair and maintain these aircraft without benefit

of complex tools, equipment, and facilities. Repair techniques need to be developed

that are simple, reliable, and easily performed with simple tools and limited access

to electric or hydraulic equipment.

0 Field-level inspection techniques and equipment need to be developed.

0 Decontamination is a requirement prior to reentry to an uncontaminated

area.

Avionics issues related to electromagnetic interference must be addressed.

Adequate techniques for handling lightning need to be developed.

The technology needs related to aviation in general are:

0 Damage tolerance and durability are safety and life-cycle issues. Damage

tolerance criteria need to be developed and validated. Programs are under way in

the Army, Air Force, and Navy to provide preliminary criteria. Updating will be

*Submitted by J. Waller and R . Ballard after the March 26, 1986 meeting to amplify onArmy activity.

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required as more and more composites are introduced into the system. Durability,

on the other hand, is an economic consideration. Criteria for durability need to be

established for long-term operations in realistic operating environments.

0 Crashworthiness designs are needed. The Army has been a leader in this

area and has developed MIL-STD-1290a that identifies criteria for crashworthi-

ness. ACAP is the first program that has required that the aircraft meet all therequirements of this standard. The design concepts used in ACAP will be verified

by large-scale drop tests of static test articles in 1987. Crashworthiness is being

considered by the other services and by the FAA.

Impact and handling damage of composites needs to be accounted for in the

initial design, taking into consideration attention to damage resistance.

0 Cost reduction is a prime consideration. Efforts to reduce material cost

need to be pursued for both material processing and volume production. More

automated manufacturing techniques are needed. In designing composites structures

the designer, materials engineer, manufacturing engineer, and the tool designer must

work as a team. A reduction in total parts count and fasteners tends to reduce costbut there must be a trade-off on size. Large parts become difficult to manage and

maintain. Although there are fewer fasteners used, the ones that are used are much

more expensive than the “penny” rivet. Fastener cost must be reduced.

0 Weight reduction is another key issue in the use of composites. Reduced

weight produces cost and performance advantages.

0 Improved material properties result in gains in strength: reductions in weight,

cost, repair, and maintenance; and improvements in safety and survivability. Some

of the properties of importance are tougher resins, higher strength, higher strain, and

improved curing properties and damage tolerance. All these factors aid in reducing

manufacturing cost.

0 Better nondestructive-testing techniques for composites are needed for qualityassurance in production as well as for field use.

0 Flammability and toxicity characteristics for composites need to be docu-

mented and solutions to related problems sought.

U.S.Navy (D . Mulville)

The major thrusts of the Navy’s composites research and development work

(military categories 6.1, 6.2, and 6.3 related to research, technology development,

and product development, respectively) were reviewed. The 6.1 work focuses on:

developinga basic understanding of composite impact damage, fatigue, fracture, and

innovative concepts for damage tolerant structures; composite structural tailoring;and metal structure crack initiation and propagation. The 6.2 work encompasses:

advanced design concepts, structural integrity, supportability, air loads prediction,

life management, and electromagnetic compatibility. The 6.3 work, not to begin until

FY 1990, will be focused on thermoplastics, toughened thermosets, and advanced

landing gears for Navy aircraft.

Some specific points are:

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About 50 percent of the 6.1effort is on composites and one-half of this effort

is with universities.

About 60 percent of the 6.2 effort is directed toward composite technology.

Due to budget reductions, out-year funding is expected to hold at $2.5 million.

The thrust of the 6.2 effort is to bring along the next generation of composites,

Le., introduce advanced design concepts for primary composite structures; reducestructural weight; increase tolerance to damage; and reduce complexity, time, and

cost of repair and maintenance.

U.S.Air Force (J . Mattice)

The organic composites program consists of four major elements related to high-

performance aircraft: (1) R&D, (2) supportability, (3) manufacturing technology,

and (4 ) structural considerations. The first three elements of the program are di-

rected by the Air Force Materials Laboratory and the fourth by the Flight Dynamics

Laboratory at the Air Force’s Wright Aeronautical Laboratory.

The major elements of each of the following programs were briefly described:

Organic Composites R b D0

0

0

0

0

0

0

0

0

0

ThermoplasticsThermosets

New polymer concepts and resin characterization

Processing science

New composites technology

Ordered polymer fiber

Ordered polymer film

Molecular compos te8

Opto-elec tronic materialsSupport activity

Organic Cornpositea Supportability

0 Advanced field repair materials

Post-failure analysis

Paint removal

Thermoplastic support

Organic C om pos ites Ma nufacturing TechnologyManufacturing science-computer-aided cure and complex shapes

0

Integrated composite center0 Large composite aircraft

0 Manufacturing for thermoplastics

Radome manufacturing technology

Composite repair center

Organic propulsion materials

Structural Considerations

0 Structural concepts

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T A B L E A -6 F A A P r o g r a m P la n s- -D e s ir ed a n d A c t u a l ($ m i l li o n )

F i sca l Year1986 1987 1988 1989 1990

D e s i r e d p r o g r a m p l a nA c t u a l p r o g r a m p l a n

S h o r t f a l l

1.9 3.9 3.9 3.7 3.20.3 0.3 1 o ? ?

1.6 3.6 2.9 ? ?

A c t u a l P r o g r a m E l e m e n tNDI (n o n d es t ru c t i v e i n sp e c t io n ) 0 .0 8 0 .1 0 0 .1 0F u s e l a g e d a m a g e c o n t a i n m e n t 0 .1 4 0 .1 3 0 .3 5S t r u c t u r a l r e s p o n s e 0.07 0.07 0.45

T o t a l ( r o u n d e d ) 0 .3 0 0 .3 0 1 oo

Structural integrity

0 Ballistic survivability

0 Repair

Specific points made were:

The level of funding identified for FY 1987 may not be realized.*

0 The program outlined represents about 140 specific tasks (projects).

0 Although work continues on thermosets, much of the effort is focused on

0 About one-third of the program is directed at supportability.

0 Decontamination, internal aswell as external, is a big issue and concern.0 The ability to repair in the field is an important capability warranting more

attention.

0 The ability to manufacture large parts is a concern.

thermoplastics.

Federal Aviation Administration (J . Soderquist)

The funded (approved) R&T program and desired R&T program were reviewed.

The program funding, noted in Table A-5, does not provide for the desired level of

R&T activity. The shortfall is roughly estimated to be some $1million to $2 million

in 1986, and on the order of $3 million to $3.5 million in later years. These data andthe actual program plan by element are shown in Table A-6.

Specific comments were:

0 At present there is an active effort to increase F Y 1987 support for the

mechanical material property testing, large fuselage decompression studies, and-*See Table A-5.

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repeated-load spectrum truncation work. How successful this effort to increase

funding will be is unknown.

In the plan, the budget numbers for the out-years are rough estimates that

do not include resources for full-scale component work, which would be costly.

Bonding integrity is an especially troublesome issue. A request for proposal

(RFP) is in preparation and should be issued in FY 1987. I t is directed at ways toexamine or detect understrength bonds. This is a first-priority project.

A second-priority continuing item of concern is failure analysis. There is also

a real need to set standards including material property testing standards. Here it

would be desirable to have NASA actively involved.

0 Cost-effective finite element matrix analysis techniques are needed as is work

to build a technology data base on fire-related material toxicity and other hazardous

characteristics associated with a crash or fire.

Damage growth analysis capability is also needed.

National Aeronautics and Space Administration (S . Venneri)The budget (See Table A-5) and plans for advanced organic composites were

reviewed in context with NASA’s aeronautics R&T budget and program strategy.Major points made were:

The funding for the advanced organic composites work in FY 1985 included

residuals from the large-scale structures program that has been discontinued. The

remaining FY 1985 funds come from the R&T base program.

The approved NASA budget reflects a $3 million augmentation for organic-

matrix composites in FY 1987. However, if these funds do not become available,

there will have to be a major reduction in the program. (It is possible that some

funds could be restored through other internal adjustments.)The broad national R&D program goals focus R&T attention on the aerospace

plane, subsonic transports (including rotorcraft), supersonic transports, and key

military aircraft technologies.

0 It is planned to increase NASA’s total materials and structures (M&S) pro-

gram (R&T base) from a level of $30 million in FY 1987 to $40 million in FY

1989. Organic-matrix composites work would decrease as a percentage of the M&Sprogram in this time period.

Composites, broadly, are to receive greater attention where they apply to

national goals related to subsonic aircraft, rotorcraft, high-performance aircraft,

and the aerospace plane.The FY 1987 budget outside of tha t related to advanced organic composites

(See Table A-5) reflects an increase of $10 million for materials and structures R&T

related to: other composite materials program augmentation, increased computa-

tional structural mechanics effort, and R&T augmentation in rotorcraft noise and

vibration.

0 A NASA advanced composites program would encompass: structural con-

cepts and sizing methodology for improved local stiffness and aeroelastic tailoring;

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development and characterization of advanced composite materials; and component

tests to verify design approaches to such items as panels, modules, and box and shell

structures.

NASA has outlined its views on “composite struc ture trends” and structured

a program chart for “advanced wing/fuselage structure R&T”; an agreed upon

program has not been identified so advice is very appropriate and useful.The budget outlook is such that it is expected that less contracting will be

supported in the next few years due to increased internal costs.

Committee Summary ofRT&D Needs and Budgets*

The committee’s summary of the RT&D needs and budget plans as expressed

by government representatives is presented in Tables A-4 and A-5.Table A-7 is an integration of the views of the government’s representatives on

R&T needs by type of activity. The government representatives’ views of important

RT&D needs reflect those identified by the industry representatives.

Tables A-8, A-9, and A-10 display integrated budget data for FY 1986 and FY

1987 as a function of program element. From these tables it is clear that the major

investment comes from DOD-some 86 percent; much of it is directed at system

and manufacturing development technology (essentially an Air Force effort), which

is considered critical to cost reduction. The NASA and FAA support , some 14

percent, is all directed to generic R&T. Although the NASA/FAA effort is shown as

being funded at the same level in FY 1987 as in FY 1986, this will depend on the

approval of a $3 million NASA program augmentation.

In FY 1987, the Army plans to increase rotorcraft R&T funding, resulting in a

significant rise in R&T funds. The Air Force has plans to increase its R&T support

for design/support and materials/manufacturing activity. The combined result isan increase in overall program funds primarily for manufacturing technology.

The government (NASA, FAA, and DOD) has pursued opportunities for joint

effort by identifying technology development opportunities in areas of common inter-

est. Over the past 10 years this joint effort has produced significant developments in

composites, including improved design and fabrication techniques, and in the basic

production of advanced organic composite structural components. This type of work

should continue, but at a higher (an order of magnitude) funding level to build the

technology base required for design, production, test , and certification confidence,

and t o allow fuller application of advanced organic composites. Program detail must

evolve from continued joint effort.

-

*This summary material was developed by the committee after the meeting on March 26,

1986.

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T A B L E A -8 G o v e r n m e n t A d v a n c e d O r g a n i c C o m p o si te P r o g r amP l a n , F Y 1986 ($ mi l l i o n )

P r o g r a m E l e m e n t sD e s i g n / M a te ri a 1 /

G o v e r n m e n t A g e n c y R & T S u p p o r t M a n u f ac. T o t a l

A r m y ( r o t o r c r a f t ) 7.7 _ _ 0.9 8.61.8a v y 0.3 1.5 --

A i r F o r c e 8.3 3.1 9.4 20.80.3A A 0.34 .9A S A ~ 4 .9

S u b t o t a l 21.5 4.6 10.3 36.4

_ _ _ __ _ _ _

a N A S A a u g m e n t a t i o n r e q u e s t of $ 3 m i l l io n i n c l u d e d .

T A B L E A-9 G o v e r n m e n t A d v a n c e d O r g a n i c C o m p o si te P r o g r a mP l a n , F Y 1987 ($ mi l l i o n )

P r o g r a m E l e m e n t s

G o v e r n m e n t A g e n c y R & T S u p p o r t M a n u f a c. T o t a l

D e s i g n / M a t e r i a l s /

-- 10.4r m y ( r o t o r c r a ft ) 10.4 _ _

_ _ 2 .2a v y 2 .2 _ _A i r F o r c e 6.0 4.3 16.5 26.8

0.3A A 0.3 _ _ _ _-- 4 .9A S A ~ 4.9 --

S u b t o t a l 23.8 4.3 16.5 44.6

a N A S A a u g m e n t a t i o n r e q u e s t of $3 m i l l io n i n c l u d e d .

Materials Manufacturing-Tailoring and Related Costs

Hercules (J. DeVault)

the state of activity and implications. It was noted that :

The presentation addressed fiber tailoring, prepreg tailoring, testing costs, and

0 Fiber strength is increasing and further improvements can be expected.

0 Fiber stiffness is improving with more gains possible.

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T A B L E A -1 0 G o v e r n m e n t A d v a n c e d O r g a n i c C o m p os i te P r o g r a m by

E l e m e n t , FY 1 9 86 a n d F Y 1987

F Y 1986 F Y 1987P r o g r a m E l e m e n t $ M i11 on Pe rcen t $Mi l l ion Pe rcen t

R&T 21.5 59 23.8 53D O D ( 16.3) (45) ( 1 8.6) (42)N A S A ~ I F A A (5.2) (14) (5.2) ( 1 1 )

Design & s u p p o r t ( D O D ) 4.6 13 4.3 10Mate r i a l s &

m a n u f a c t u r i n g ( D O D ) 1 0.3 2 8 1 6.5 3 7To tal 36.4 100 44.6 100

a I n c l u d e s N A S A r e q u e s t of $ 3 m i l l io n a u g m e n t a t i o n .

Material costs ($ per pound) are still coming down for current materials

and significant drops in cost can be expected for advanced materials with increased

product ion volume.

On the basis of unit price per modulus/density, advanced fibers are projected

to be equal in cost to state-of-the-art fibers, and on the basis of unit price per

strength/density, advanced fibers are projected to have a slight cost advantage.

Higher filament count material has a lower cost.

The factors affecting prepreg costs are: weight, resin content, width, and

automatic tape-laying machine grade. Their effects are: (1) lower weight is morecostly, (2 ) process cost increases with lower resin content, and (3) automatic tape-

laying grade increases cost (compared with hand laying).

Prepreg tow has the potential for being the lowest cost material form.

Matrix tailoring will impact prepreg prices. Thermoplastics are projected to

be priced in the mid-range of thermosets and both are projected to come down in

cost. The types and number of tests per material lot affect costs. Holding tests down

in production will hold costs down, but tests are a small part of the price structure

(about 3 percent for fiber, 5 percent for prepreg).

Increases in the number and types of tests being specified for new products

result in higher materials costs.

In summary, as the field matures there is more tailoring of material. This

has resulted in an increase in material costs. The suppliers are responding with

improvements in manufacturing techniques to produce better products and hold

costs down. This improvement trend holds promise for slowing the rate of cost

increase. Costs may go from $l/pound to $2-$3/pound. It is possible the number

and/or frequency of testing could decrease with more production experience.

The Navy is selecting material specification and requiring two material sources.

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In response, Hercules is working with Fiberite to produce specified material. This

has required the complete transfer of related material processing and manufacturing

technology.

It is believed that material-processing specificationscan be tightened further (to

f 1.5 percent) resulting in lower handling/manufacturing costs for the user. It is

believed that the materials manufacturers are working on the problem of materialtolerances and tha t government assistance in this area is not required.

Logistic Support

Military service representatives from the Navy/Marine Corps,Air Force, and

Army briefed the committee on field experience with aircraft composite structure

repair and maintenance.

U.S. Navy/Marine Corps (J. Meyers)

Most nonstructural damage is reasonably handled in the field. However, struc-

tural damage is an issue requiring innovation and care and is generally not fully

manageable in the field. As experience grows with composite repair and mainte-

nance (R&M), information is being fed back t o the manufacturers so that R&M is

accounted for in design.

Techniques for obtaining three-dimensional “pictures” of hidden damages are

being developed. These techniques show promise for internal damage diagnostics.

The basic problem for R&M is the ability to perform in-field work with limited

support skills and tools. The Navy has developed a list of “future considerations”

relating to what needs to be done and what can be done to improve field-based

R&M.

U S . Air Force (J . Harrington)

A t the depot level, composite structure repair and maintenance can be handled

reasonably well. But, there is concern about the ability to do the required work

in the field. Of interest is quick, simple, effective repair capability. Supportability,

related to R&M has been elevated to an important design-selection consideration.

From a design standpoint, items of concern are damage containment and associated

delamination and blowout. The service is also directing attention to standardization

of approaches to and equipment for repairs.

An obvious major issue is quickly getting aircraft back into service, which points

to the need for an effective field repair capability.

There is a renewed interest in honeycomb structures. This is due to an mproved

ahility to eliminate surface microcracking, thus controlling moisture intake and

avoiding delamination and internal metal corrosion.

It is forecast that in the next decade some 50 percent of the structural weight

of Air Force advanced tactical fighter (ATF) aircraft will be composites. These

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structures have to be supportable (in the field and at depots). Supportability re-

quires design for inspectability, maintainability, repairability, and replacement. The

enemies of supportability are environmental, service, and battle damage.

U.S. Army (T. Condon)

Major concerns related to composite structures are reliability, maintainability,

and repair. Much of the noncombat problems are associated with work accidents, i.e.,

dropped tools and cart strikes. The Army has supported a number of studies directed

at designing for inspection and R&M to reduce the impact of these problems. The

philosophy is to consider R&M in design and design to allow field-level R&M. This

approach must consider field skills and resources including limited environmenta1

and quality control and such things as repair with dry materials and two-part epoxy

resin, repairs with hand-formed metal parts, and modular repairs.

Some areas warranting future research and development include:

Field repair kits;High-temperature materials repair;

Generalized equipment for heat and pressure application;

Portable nondestructive inspection equipment and techniques;

Damage resistant and tolerant R&M design; and

Damage assessment, test, repair, and retest.

These matters are to be addressed, to a degree, in an R&M program currently

under development.

An Army-sponsored program developed inspection and repair techniques for a

full-scale composite rear fuselage section of the UH-60 helicopter. This work has

shown tha t with appropriate basic design, primary s tructure R&M can be handledin the field, but with some weight penalty. Repair kits need to be developed as do

related heating and vacuum devices. However, there is a need for new personnel

skills and training. Specifically, the R&M program found tha t: mechanical splicing

was of high quality, repairs exceeded strength requirements, quality of repairs were

verified by inspection, cosmetics were acceptable, and field repair was feasible.

Airline Perspective

The Kuperman/ Wilson (United Airlines) report of 1977detailed early airline ex-

perience with organic composite secondary structures.'* The committee was briefed

on more recent airline experience. An update on airline views is contained in the Air

Transport Association (ATA) letter presented in Appendix B.

Delta Airlines (C . Walker)

Weight saving is the interest that drives manufacturers and buyers to compos-

ites. However, safety, serviceability, and maintainability remain important consid-

erations.

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97

honeycomb structures, serviceability and life have been serious problems.

Surface cracking, water ingestion, delamination, sealants (resealing), and inspection

are real concerns and problems. Stiffenedgraphite composite panel structure (rather

than honeycomb) may be the way to go, but this may mean added weight. There

has been limited experience with graphite in airline applications.

Other areas of concern for the airlines are fatigue resistance and damage growth.

These factors are understood for metal structures but not well understood for com-

posites, so for metals there is a high level of confidence. Much more experience is

needed with composites to build the same level of confidence. Pa rt of the problem is

the need for good inspection techniques other than “coin banging.”

The move to larger structures will bring forth problems of repair. What will be

desired are repairable composites, designs that do not require special tools, skills, or

support equipment.

The Kuperman/Wilson report still reflects the state of affairs today regarding the

kinds of problems the airlines face with composites. However, the yearly operating

costs associated with each pound of aircraft weight makes weight saving of serious

interest and composites a competitive material. For a 727, $18 per pound is theincremental cost of fuel; for the Delta fleet, incremental costs range from $12 to $24

for fuel per pound of weight per year.

Mr. A. Tobiason, of the ATA, invited guest of the committee, reported on

recent environmental experiences with composite structures. A lightning strike on

an aileron destroyed it and it took 5 days and 80 working hours to repair the aircraft

at the airline maintenance center. On another aircraft, hail damage required the

return of the aircraft t o the manufacturer for repair.

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Appendix BCorrespondence-Air Transport Association of America

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Air Transport Association a h OF AMERICA

1709 New York Avenue, NWWashington, DC 20006-5206Phone (202) 26-4000

December 19, 1986

Hr. Bernard MagginAeronautics and Space Engineering BoardJH 413

National Research Council

2101 Constitution AvenueWashington, D.C. 20418

Dear Bernie:

The purpose of this letter is to provide you with furt her informationfor use in the NRC AD hoc Committee fi nal report to NASA on the Status

and Viability of Composite Haterials for Aircraft Structures. At your

suggestion, we asked several ATA member airlines to update the 1977 S M P E

paper&/.on the NRC study.

As yo u will recall, three airlines have made earlier comments

The airlines generally believe that notwithstanding efforts by the

airframe manufacturers , their most recent technology transports are stillshowing problems that i n di c at e a ny f u t u r e R W p r o gr a m r e co m me n de d b y t h e

NRC Comm ittee should include detailed attention to conditions experiencedby the operators of ne w technology aircraft. The current list of

problems is not much different f rom those discussed in the SMPE paper.

One way to put it is: can ne w technology reduce the overall

cost-of-ownership? From listening to the DOD briefers who operate

advanced aircraft which incorporate composite materials one wouldconclude that their operating and maintenance difficultie s are similar to

those of th e civil operators.

Airlines operating the most recent domestic technology aircraft

provided ATA with the following specific comments.

"We have observed the following problems in our present aircraft

composite structure which are basically graphite/epoxy and

graphite/kevlar/epoxy construction:

-/ "Today's Non-Hetallic Comp osite Airframe Structure -- An Airline

Assessment" by H. H. Kuperma n and R. G. Wilson, of United

Airlines.

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1. Paint and resin matrix cracking leading to water

ingestion and freezelthaw delamination

2. Lightning strike damage

3. Inadequacy of aluminum flame spray lightning protection

4. Abrasion/erosion damage

5. Foreign object impact damage

We have observed these problems over a period o f 4 years. Webelieve 3-5 years are sufficient to disclose operating problems

pertaining to composite structure.

One general problem with composite panels is erosion of theleading edge on external panels.

fan cowl doors, landing gear doors and wing leading edge

panels. Erosion typically starts at the forward edge andextends back one quarter inch or more, involving several pliesof material. If damage is not t o o severe, the panel edge may be

smoothed by chamfering, then applying an epoxy resin to seal theexposed grain. A possible production improvement would be to

wrap the edges of composite panels with a stri p of fiberglass so

that the end-grain is not exposed to wind and moisture.

The worst erosion is seen on

Another problem inherent to Kevlar composit e panels is water

ingestion. Although we have had no discrepancies reported on

one ne w technology aircraft to date, we d o have experience on

another new technology aircraft to draw from. Kevlar panels

must be topcoated with a flexible polysulfide sealer to preventwater ingestion. Unsealed panels can ingest detrimen tal amounts

of water after only 12 to 24 months in service.

Refinishing Kevlar panels previously topcoated with polysulfidesealer is another problem. It is difficult to scuff-sand the

panel without sanding into the sealer. When this happens, theentire sealant coat must be sanded off. Sanding pads must be

changed frequently since the sealer tends to gum up the pads.We d id not want to use a sealant to p coat in anticipation of the

refinis hing problem. However, in order to preserv e the warranty

provisions, we have continued t o use the sprayable sealant

topcoat.

Another potential problem with composites was discoveredrecently during our initial ultrasonic inspecti ons of rudders

and elevator s using recommended procedures. The ultrasoundsignal was attenuated (absorbed) over much of the inspection

area to the extent that t he inspection could not be completed.

Th e aircraft manufacturer recommended that we revert to visual

and coin-tap inspections.

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By design, composites tend to be dry (having the minimum

acceptable amount of resin) in order to conserve weight. This

may create tiny voids or air pockets which may attenuate an

ultrasound signal and/or make the panel more suscepti ble tomoisture ingestion and leading edge erosion. The composite

ultrasound calibration stand ards provided by t he manufacture rwere manufactured with generous amounts of resin and yield

excellent test reading.importance of establishing and maintainin g quality con trol in

manufacturing, which may be more difficult to achieve in

composites.

This particular comment points out the

In order to enhance future applications of composites,manufacturers should emphasize quality control, reliability and

maintainab ility. Weight savings loses its significan ce if the

structure cannot be maintained."

Another area mentioned by the airlines is the infrequent necessi ty,but cost ly in terms of the lost revenue, to ferry an aircraf t from a

field station to a major rep air facility having appropriat e capabilities

to repair damaged composite structures.

A previous ATA le tter to you discussed some safety considerat ions

worth examining in future R&D for use of composite materials in major

fusel age and wing stru ctures -- crash-impact dynamics and

fireworthin ess. As in other new technology areas, the excellent safety

record of existing technologie s should be maintained or enhanced, if

economicall y possible. It is our understand ing that the existing NASA

composites program contains little, if any, specific safety content. On

the other hand, the F A A has a limited safety program devoted tocomposites.

T h e NRC Committee may wish to consider a recommendation for

development of a joint NASAIDODIFAA-industry (manufactur ers, vendors,

airlines, DOD) program that encompasses pertinent maintenance and safety

aspects in addition to performance objectives.

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